Change IPsec destination port

Hi Everyone, 

We need to established a vpn connection with a partner. However he requested that the external port be different that standard ike port 500, 4500. The unit I need to connect to is behind a nat and the client is doing port translation. 

external port 40500 ==> internal port 500

external port 44500 ==> internal port 4500

Is there anyway I can specify different destination port in the ipsec configuration, is this something possible to use different communication port for ipsec?  

Thanx!