I am considering doing this with one of the next coins I add, with PPS as the payout method.  You would submit shares in that currency and get paid per share in LTC.

However, I would not be able to do this fee-free, there will likely have to be a 2-3% PPS fee (which certain members would be exempt from) as well as some kind of exchange fee to mitigate my risk in exchanging a potentially volatile currency for a stable one.  This would free users from having to maintain so many wallets and not having to worry about exchanging their coins.  If it works out well with the new coin I would likely move most of the coins on the pool to the new payout method.  Stay tuned.