Fragmented packet to jumbo frame - Balance 2500


When we get fragmented packets through the vpn tunnel our balance 2500 reassemble it to a jumbo frame before passing it on. This is a problem to us when our network dosen´t allow jumbo frames.
We have tried to play around with diffrent mtu values but with no success. How can we get the balance router to pass on fragmented packets?
This is how it looks today: