Given rectangles with text:

\starttext
Before:\\
\startMPcode
draw unitsquare xscaled 2cm yscaled 1cm;
\stopMPcode
\\
After:\\
\startMPcode
for i=0 upto 1:
draw unitsquare scaled 1cm xshifted i*cm;
endfor;
\stopMPcode
\stoptext

How can a line be drawn connecting the right edges of the rectangles? I have played with:

\startuniqueMPgraphic{line}
path a;
a:=(0,0)--(0,3cm);
draw a withpen pencircle scaled 3pt withcolor green;
\stopuniqueMPgraphic

\defineoverlay[line][{\uniqueMPgraphic{line}}]

and using it in \framed, but placing the line correctly is elusive.