The Stargate audios have had both Canadian and British actors in the same audio, so it wasn't outside the realm of possibility.
When did Stargate get audios?
http://www.bigfinish.com/Stargate-SG-1-and-Atlantis
Big Finish released six one-hour audios last year; three for SG-1 (starring Daniel, Daniel & Vala, and Dr. Frasier) and three for Atlantis (starring Weir, Beckett, and Zelenka).
The fourth SG-1 audio was originally announced as one starring Janet Frasier and Teal'c, but it would appear to have been replaced with a Teal'c-centric audio.
^When you only have to pay one major actor, therefore have less post-production, and can charge more per disc, the realm of possibility is rather different.
That's true, though I have to imagine that he could have recorded his lines separately from the other actors, even though that's not what Big Finish normally does. Ah, well, I haven't listened to the audio yet, so I can't judge it.