You could have the summoned whatever make an automatic grapple check to represent the target needing to get out from under it. Inanimate objects would just get their size bonus to the check (it's hard to get out from under a piano that's fallen on top of you, but much easier than getting out from under an angelic buffalo that's fallen on top of you).
Sounds good to me...
Running: Ruceeglaelsktinag ICOOCMap
My Dream Campaign: ICOOC No Map Right Now.
For everything else (including my extensive homebrew) see: Extended Signature My Homebrew is meant to be used, but, if you do, PLEASE tell me how it goes.