Allow all unidentified traffic in isa 2004

I'm  trying to create an access rule to allow all unidentified traffic in isa 2004.  This may sound strange i know but let me try to explain.
We have a internal networks defined as 192.168.111.0 to 192.168.111.254 and 192.168.1.0 to 192.168.1.254.
The 192.168.1.0 network is attached to internal network through a MPLS connection via  a cicso switch which dosn't go through ISA . So traffice from our MPLS connection isn't going through our isa but traffic going to 192.168.1.0 network does then through our ISA connection here lies the problem ISA is blocking this traffic. ISA logs states denied connection.
We have a work around by seeting printer , defualt gatways to be the MPLS IP but we won't to use ISA , How can this be done.
Cheers.