Uh, yeah that might be a problem. However, just to take this out of the way, there are two relevant notes on the Wormhole page [1]:
Q. What are good buffer settings for Wormhole2?
Q. How do I get the lowest possible latency for a "live" connection (direct mode)?
Moreover, before I get to the driver part, it seems that in the freeware, independent from Reaper, plug-in package [2] there is a Wormhole equivalent "ReaStream".
What about
:
1) Muting the master output? (Might require additional routing to some kind of a master bus?) Maybe somehow routing the tracks in the DAW to a bus that's routed to "none"??
2) Disabling the audio interface in the device manager? You can try, though I doubt

3) Googling "dummy audio driver" yields somebody's intriguing advice in some newsgroup:
There is no dummy audio driver, but perhaps installing a driver for an audio device that doesn't look very hard for it's hardware might do the trick. Presonus Firepod comes to mind but I'm not sure if they have a 2003 driver. M-Audio Firewire 410 is another contender.
4) ASIO4ALL? (Now you're gonna settle with that without the networking eh?

)
5) JackDMP's ASIO driver, possibly with everything disconnected in the routing dialog (LOL that's geeky).
[1]
plasq.com - Wormhole2 PAQ
[2]
REAPER | ReaPlugs