how can i create a variable size Buffer?

Hallo, when i run my Simulink model, i get an Error with the Buffer Block as shown in the capture (Buffer does not support variable Size signals).

i want to create a non overlapping variable Size Buffer, which adds the remaining overflow 'z' in the beginning of the next frame.

Can anyone give me tips on how to do it and help me in anyway.

I appreciate every help. Thanks in advance!