Add space in brqalign

Some time ago David Carlisle wrote an awesome brqalign function in this answer: http://tex.stackexchange.com/a/51543/4011. See the cited code below.

How can I add space between the rows of brqalign?

\documentclass{article}
\usepackage[leqno]{amsmath}

\renewcommand\theequation{\alph{equation}}

\newenvironment{brqalign}{%
% START CODE
%%%%%%%%%%%%
% Do everything an a box, as you can not remove
% things from the main vertical list.
\setbox0\vbox\bgroup
% Allow \\ for ends of row.
\let\\\cr
% Use an \halign (I experimented with using one
% of the AMS alignments but they tend to want to
% be full width, or already in math mode, so just
% use a primitive \halign here with two display math
% entries in its preamble.
\halign\bgroup
\hfil$\displaystyle##$&$\displaystyle{}##$\hfil\cr}%
{%
% END CODE
%%%%%%%%%%
% Finish the \halign.
\crcr\egroup
% Now, at this point the vertical list being assembled in
% box0 contains all the rows of the alignment these will be
% a sequence of \hboxes (which will all be forced to be the
% same width) and baselineskip glue. (While testing with the
% AMS alignments there was additional glue and penalties
% as well.
%
% We will discard all the glue and penalties but assemble
% a horizontal list of the boxes in box1.
% start by making box1 and empty hbox.
\global\setbox1\null
% Then loop backwards up the vertical list discarding any glue
% and penalties and grabbing hold of each box.
\loop
% This combination removes two adjacent glue items
% or glue followed by penalty, it may be more than needed
% but better be safe than sorry.
\unskip\unskip\unpenalty\unskip\unpenalty
% Glue and penalties we discard, but the boxes have the
% formula so remove this one from the current list and
% save it in box 4.
\setbox4\lastbox
% If there was no box box4 is void and we reached the top
% of the original vertical alignent so stop.
\ifvoid4
\else
% Otherwise Put this box4 at the front of the horizontal
% list being built in box1, followed by an em of space.
\global\setbox1\hbox{\box4\hskip 1em\unhbox1}%
% Go round the loop again.
\repeat
% End the group for the working box 0.
% The horizontal list is globally assigned
% to box 1 so will be visible after this group end.
\egroup
% Now put out all the boxes flush left, the usual paragraph breaker
% will fit as many on a line as it can. As each box is the same width
% vertical alignment is automatic.
\begin{flushleft}\unhbox1 \end{flushleft}%
% Ignore white space after the end of the environment
\ignorespacesafterend
}

\begin{document}

\begin{brqalign}
x^2 + y^2 &= 1\\
a + b &= c\\
r-x &= y+z \\
f - y &= z\\
a - b &= 2d\\
r+x &= 2y-3z
\end{brqalign}

\end{document}

-

\begin{flushleft}\setlength\baselineskip{1in}\unhbox1 \end{flushleft}%

Thanks. However this also added space before the first row so I did something like this: \vspace*{-3ex}\begin{flushleft}\setlength\baselineskip{6ex}\unhbox1\end{flushle‌​ft}. This is sufficient for my purpose but as you see I had to use -3ex and 6ex i.e. different numbers which seems not to be very elegant –  student Mar 13 '13 at 20:21
well latex list environments do something similar internally just hide it behind top level parameters for space before item etc. the list is set as a paragraph and at the primitive Tex level baselineskip is always constant for a paragraph (the value at the end is what counts) so to make a nicer top level interface you'd probably always subtract the new \baselineskip at the top and then have a second parameter +3ex in your case documented as the space before the display. –  David Carlisle Mar 13 '13 at 20:26
Why doesn't a simple \linespread{1.5} work?? –  Hendrik Vogt Mar 13 '13 at 20:29
@HendrikVogt it does, it's just another interface to setting baselineskip \linespread{2}\selectfont\begin{brqalign} will work but you'd need to group it or set it back at the end, or you could set that inside the definition where I set baselineskip directly. –  David Carlisle Mar 13 '13 at 20:36
@David: Oh my, \selectfont - smack! (It is a somewhat mean design decision that \selectfont is required here. Am I the only one who always forgets it?) –  Hendrik Vogt Mar 13 '13 at 20:44