So you simply need to move the stack pointer by adding the stack frame size to the stack pointer using ai $sp, $sp, FRAME_SIZE.

mwarn-framesize=framesize and -mwarn-dynamicstack: These options cause a compile-time check whether a function exceeds a given stack frame size or uses dynamically sized stack frames.

You might wonder why I check whether the method is static at the start of my parameter size calculation, then initialize the stack frame slot to zero if it is (as opposed to one if it is not).