full screen app overlaying split screen apps?

hey folks,

longtime user, first time caller.  thanks for the great work--i've used
ratpoison for years and have found it perfect for my mouseless needs.

i've recently started living in a splitscreen world with my IM client in
a small slit at the bottom of the screen.  unfortunately it takes some
doing to get it to come up right (text based client, inside screen, in
an xterm), and it doesn't resize well (it's curses and doesn't take
SIGWINCH quite right, at least not under screen, which is a requirement).
so i'd like to leave that window alone and never resize it.

the challenge comes in running VirtualBox, which reallllly wants to be
full screen.  ratpoison handles it well, but VirtualBox sometimes fails
to realize the true window size it is in (the top 4/5 of the screen) and
draws off the bottom of the viewpane as though it were fullscreen, which
is fairly inconvenient.

so, my question is, is there a way to tell ratpoison to let an app to ignore
the split and go fullscreen despite there being a window in the split
that isn't going anywhere?

thanks for your advice!