Change the size of Compose window?

[lf11 naisp net]

I've got this dinky little 15-inch monitor running 1024-768 ... and
although the compose window does fit, the proportions are way off.  Any way
I can change the window width without source-hacking?  Seems the minimum
width is 869...

Something closer to half-the-screen.  I realize that one the required
uber-geek hardware pieces is a 20+ inch monitor, but that ain't happening
this month here!

Thanks
--lf11