how to change MS IAS PROXY-STATE length

hi,

i need to have a RADIUS server as Proxy RADIUS Server like below topology:

   NAS <---> MS Windows2003 IAS(Proxy RADIUS) <---> nttacplus(main RADIUS)

but there is a problem, when IAS proxy RADIUS forward an ACCESS-Request with 10 octet PROXY-STATE length to the nttacplus RADIUS, the nttacplus reply ACCESS-ACCEPT with first 6 octet of received PROXY-STATE, so the IAS proxy RADIUS doesn't accept the message and try to send similiar ACCESS-REQUEST for another two times.

is there any way to reduce the PROXY-STATE length to 6 octets in MS IAS proxy RADIUS?

if no, is there any way to solve the problem?