Removing from the lua stack manually


I've got a problem:

I'm calling C from Lua with arguments then popping something onto the stack and calling a Lua function with the arg. But the previous arguments are still there so Lua gets confused and does nothing.

I looked around and lua has a lua_remove function to get rid of things from the stack but it seems we don't have access to that with the SDK. Is there another way of doing this or is it just not possible right now?