Registering two VOIP service to same provider

I read the FAQ, knowledge base, docs, forums and google and could not find an answer to my predicament. Here it goes. I am using Asterisk on Linux.

I have two VOIP services from the same provider defined. I have defined two channels in my sip.conf (say serv1 and serv2) and have two register statements one for each services. The issue is that incoming calls can only be received by one service because my provider does not permit having two registrations to the same ip address/port combination(my speculation founded on the fact that either services can receive calls when only 1 registration is active). I only have 1 ip address so what I would like is to have my provider send calls to serv1 on default port 5060 and calls to serv2 on port 5061. I believe that in order to do this the via: header on the register statement must specify port 5061 for the register for serv2. I thought that the port statement in the peer definition for serv2 did that but apparently not.

Can someone help me. Thanks.

Can you configure you provider to forward serv2 to serv1 ?

I cannot forward serv2 to serv1 because they are different clients and serv1 cannot be tied up handling serv2 calls.

It was purely technical question.
Can your provider do this?