How to restore an unbuffered frame based signal to its original frame length?

In Simulink, when processing frame based signals through blocks which only accept the sample based ones (as look up tables, in my case) an unbuffering operation is needed first. But how to restore the original frame length after processing?

The Buffer block requires as input the desired output frame length, but I want it to be determined at runtime, since by using my subsystem in different contexts, the original one can be whichever.

Thanks in advance for any help, Luca