[SR-Users] number based routing and NATed peers

Hello, Im gathering ideas about routing based on caller number to multiple peers and -lets say- subscribers. As far as i know we can route the calls with LCR based on prefix or the whole number to the LCR gateways which are specified in the LCR module gateway table. This is working very well with public IP based "peers". We can route calls to these gateways. But what can we do if we have to route to a "peer" which is behind NAT. Basically they have to REGISTER as a subscriber, but we cannot add a subscriber to the LCR gateway table, beacuse LCR module needs a directly reachable IP address with a fixed port. Does anyone have any ideas on how to handle these mixed type peers? Or maybe we have to add the fixed IP peers which are not REGISTERing to the usrloc database somehow and then we can do a lookup location based on $rU. To make myself clear, it would be nice if we can handle those 2 types of our peers unifromly in terms of SIP routing, thats why im looking for a "unified" solution. Thanks for your suggestions. With kind regards, Zoltan