[RP] forced shrink

[Aaron Griffin]

Hello,
I'm curious if it is possible to :shrink a window regardless of
transient/nontransient/however it works now.  As it stands, I rarely
feel the need to :shrink a window, unless I have something
fullscreened that I'd rather not have.  At that point, shrink fails. 
I'd like to, basically, resize all sides by -X, so I can manually
shrink a given window.

If anyone knows if this is possible, let me know.  I'd be willing to
code something up, but I'd like to see if it can be done with existing
features before I do that.

Thanks,
Aaron