supporter advertising for mobile

so i'm playing around wpms mobile edition plugin + carrington. not activating it on main blog, but allowing sub blogs the option of activating it. re: the supporter advertising plugin, right now i'm running a simple 468x60 banner (any larger banners would run into trouble if users select certain themes). on the mobile site, of course the 468 banner is too large.

is there any way, even if it's a plugin file hack, to make a conditional saying something like "if mobile browser x, y, and z, then return ad code 2"?

i'd like to have google mobile ads showing up instead. besides the style issue, there are financial considerations. for me, historically, google mobile ads have 4-6x the ecpm as traditional banners, so i definitely don't want to leave $$ on the table...