(Note: it's a community answer because original idea is from Tom Bombadil.)
Here is a variant of Tom Bombadil's answer with a few improvements:
The two macros are named \topmarginpar
and \botmarginpar
as requested.
Their first argument (optional and empty by default) is some options for the TikZ node (to allow filling, drawing a border, etc.). Their second argument is the content of the paragraph.
There are some calculations to correct a bug of tikzpagenodes
with even page (edit: Martin Scharer is very reactive: a version with bug fixed is coming to CTAN.).
The code uses let
operations (and calc
TikZ library). I think it is more readable than PGF calls.
Limits:
\botmarginpar
should stack paragraphs in reverse order!
- If a stack is full, it does not continue to the next page. It overflows up or down the page.
- If
\topmarginpar
(or \bormarginpar
) is called in the last paragraph of a page, the margin paragraph can appear on the next page and not in the right order.
Here are two pages (odd then even):

The code (with my comments):
\documentclass[twoside]{report}
\usepackage{tikzpagenodes}
\usepackage{xifthen}
\usetikzlibrary{calc}
\def\myyshifttop{0}
\def\mypagetop{0}
\newcommand{\topmarginpar}[2][]{% tikz options of node, content
\begin{tikzpicture}[remember picture, overlay]
% reset position on new page
\ifthenelse{\thepage=\mypagetop}{}{\xdef\myyshifttop{0}\xdef\mypagetop{\thepage}}
% a big path with many actions
\path let
% patch for bug in tikzpagenodes with even pages
\p1=(current page marginpar area.north west),
\p2=(current page marginpar area.north east)
in \pgfextra{
\pgfmathsetmacro{\xw}{\x1<\x2?\x1:\x2}
\pgfmathsetmacro{\yw}{\y1<\y2?\y1:\y2}
\edef\coord{\xw pt,\yw pt}
}
% draw topmarginpar
node[below right, yshift=\myyshifttop, text width=\marginparwidth-4pt, inner sep=2pt, #1]
(tempnode) at (\coord) {#2}
% next position
let \p1=(\coord), \p2=(tempnode.south west) in \pgfextra{
\pgfmathsetmacro{\diffy}{(\y2-\y1)}
\xdef\myyshifttop{\diffy}
};
\end{tikzpicture}%
}
\def\myyshiftbot{0}
\def\mypagebot{0}
\newcommand{\botmarginpar}[2][]{% tikz options of node, content
\begin{tikzpicture}[remember picture, overlay]
% reset position on new page
\ifthenelse{\thepage=\mypagebot}{}{\xdef\myyshiftbot{0}\xdef\mypagebot{\thepage}}
% a big path with many actions
\path let
% patch for bug in tikzpagenodes with even pages
\p1=(current page marginpar area.south west),
\p2=(current page marginpar area.south east)
in \pgfextra{
\pgfmathsetmacro{\xw}{\x1<\x2?\x1:\x2}
\pgfmathsetmacro{\yw}{\y1<\y2?\y1:\y2}
\edef\coord{\xw pt,\yw pt}
}
% draw botmarginpar
node[above right, yshift=\myyshiftbot, text width=\marginparwidth-4pt, inner sep=2pt, #1]
(tempnode) at (\coord) {#2}
% next position
let \p1=(\coord), \p2=(tempnode.north west) in \pgfextra{
\pgfmathsetmacro{\diffy}{(\y2-\y1)}
\xdef\myyshiftbot{\diffy}
};
\end{tikzpicture}%
}
\usepackage{lipsum}
\begin{document}
\topmarginpar[red,fill=yellow!30]{On a journey to find the cure for a
Tatarigami's curse, Ashitaka finds himself in the middle of a war
between the forest gods and Tatara, a mining colony.}%
\botmarginpar{What begins as an open and shut case of murder soon
becomes a mini-drama of each of the jurors' prejudices and
preconceptions about the trial, the accused, and each other.}%
\lipsum[1-3]%
\botmarginpar[font=\itshape\footnotesize,text=green!50!black]{The
defense and the prosecution have rested and the jury is filing into
the jury room to decide if a young Spanish-American is guilty or
innocent of murdering his father.}%
\topmarginpar[blue]{In this quest he also meets San, the Mononoke
Hime.}%
\lipsum[4-7]%
\topmarginpar[red]{On a journey to find the cure for a Tatarigami's
curse, Ashitaka finds himself in the middle of a war between the
forest gods and Tatara, a mining colony.}%
\botmarginpar[orange!50!gray]{What begins as an open and shut case of
murder soon becomes a mini-drama of each of the jurors' prejudices and
preconceptions about the trial, the accused, and each other.}%
\lipsum[8]%
\topmarginpar[blue]{In this quest he also meets San, the Mononoke
Hime.}%
\botmarginpar[green!50!gray]{The defense and the prosecution have rested
and the jury is filing into the jury room to decide if a young
Spanish-American is guilty or innocent of murdering his father.}%
\lipsum[9-12]
\end{document}
memoir
class has has\sidebar
which looks like your\topmarginpar
plus it has\sidefootnote
which looks like a numbered version of your \bottommargin` macro