Using Calling-Station-Id or AcctSessionId as NAS-Port

I need to use Calling-Station-Id (or AcctSessionId) as NAS-Port and provide dynamic Ips using rlm_ippool. Using attr_rewrite it´s possible to make this change (Calling-Station-Id => NAS-Port), but the freeradius/modules C code define port as int. My calling-station-id have 15 numerics chars of size. Have anyone any idea ? Thanks Toledo