Was looking at the Swiss Rifles forum(which has a whole section on reloading) and ran across a link to this at Surplusrifle.com on the subject, which includes the hydraulic depriming tool the guy built.
I've tried the hydraulic method(makes me very glad I picked up that RCBS berdan depriming tool when I ran across it). But, while messy, it does work.
In connected news, I found a few brass 7.62x54r cases which have the 'nny' headstamp(PRVI manufacture, I think), deprimed, and tried one with a berdan primer; it went in with very little pressure, so little that I would not fire it as there's no way the thing seated tightly enough to prevent gas leakage. Though 'flood' might be a better word in this case. Might work in cases of some other manufacture, if I run across some I'll see.