Once you have a VPN set up, you could park a couple remote desktop sessions in the office and the remote employees can run the application that way.

Where you park the sessions is flexible: I've seen offices with a couple older computers on a KVM switch. It was ugly, but it worked. Just needed someone to occasionally power cycle the machines if they hung.

Haven't worked with anything recently from them, but Watchguard had some really easy VPN hardware.

-jk