Assuming you don't feel like managing all external FooSystems.com addresses internally, you can do the following:
On your internal DNS server, create a new *zone* "test1.foosystems.local".
In that zone, create a new host (A) record, leave the name field *empty*, just enter the internal IP address. This will create a "Same as parent" entry.
On your client, run an
ipconfig /flushdns
and from now on, "test1.foosystems.local" (only) should resolve to your internal IP.