Well, he can be very convincing, that's for sure :)
Right now I've fallen behind on this show (I stopped listening sometime around episode 15) but I will rectify it in summer - it's perfect when hiking ;)
I used to follow Snapecast pretty religiously last year and remember some very good imitations from the early episodes - I'm sure back then, aside from regular Snape, Chris imitated Hagrid, Dumbledore and Lockahrt, did a spectacular Lucius (with a faux-French accent! Definitely worth listening to!) a very Fiennes-like Voldemort... And I know there were more. If you don't have time to catch up with 20+ past shows, you can check transcripts on their Livejournal page, see who's on the agenda in the Owl Post segment of each episode and downlowd only those episodes that sound most interesting.