You can always just setup an outbound NAT rule on the load balancers for the "server1" and the other servers. Add a route on "server1" for the Cloud Application destination that points to the floating self-IP on the LTM pair.
Alternately, you could make the LTM floating IP the default route for the servers that need to reach the Cloud Application. The NAT rule on the load balancers would be the same.
I would avoid trying to create a Virtual server on the LTM for the Cloud Application. Simply because you are load balancing across a WAN (performance concerns with scalability) and you have no control over the remote services.
But this NAT setup can be done with most firewalls and do not necessarily require an F5. Unless the F5 is already being used in this capacity, you might be better off getting NAT done by the firewall team.
Jason