Hi,
I think you can't do that on pre-8.3, but you might try something similar to the following on post-8.3, I have never used it on real life scenario, but it might work:
object network HOST1
host 192.168.1.1
object network HOST2
host 192.168.1.1
object network MAPPED1
host 50.50.50.50
object network MAPPED2
host 50.50.50.50
object network HOST1
nat (inside,outside) static MAPPED1 service udp 8000 8000
object network HOST2
nat (inside,outside) static MAPPED2 service udp 8000 4569
Regards
Aref