Multiple prefix for outbound

Good day,

We have do a lot of site to site calling based on 4 digit dialing and many DID's

I need to be able to add multiple prefixes based on the 4 digit number dialed.

Example
Internal ext
32xx
34xx
43xx

Site 2
50xx dials 1 555 49xx
51xx dials 1 555 51xx

Site 3
39xx dials 011 44 5555 55xxxx

So to dial site 2 when someone dials 50xx i need to remove the 50 and insert 155549xx
for 51xx remove the 51 and add 155550xx

For site 3 when someone dials 39xx add 0114455555539xx

I setup another outbound route - Dial_Site_2
50|xx
51|xx
but how do i insert the prefix.

I only have one outbound trunk, I created a few more and added the prefixes but they are all labeled the same "ZAP g1", so I gather there is a better way to do this.

PS, I have 15 different prefixes that I need to add so a nice easy way to manage this would be good.

Thanks.