marginpar anchored by pages not by text

I'm using marginpar to put margin figures in a document - there are $n$ pages and $n$ figures so I'd like to have one on each page, anchored to the first line of text on each page - at the moment I put them in in roughly the right place with

\marginpar{
\begin{figure}
\includegraphics[angle=270,width=\marginparwidth]{images/diagram.pdf}
\caption{mycaption}
\label{mylabel}
\end{figure}
}

but when I add or remove text they get moved around unpleasantly - is there a way I can enforce with say \marginpar[page=1]?

You can not put a figure in a marginpar; your posted code would produce the error

! LaTeX Error: Not in outer par mode.

To include an image at the same point in each page you could use something like

\makeatletter