This is my method also, although I never, ever have anywhere near as much cash left over as the OP does. I can't imagine changing/withdrawing that much currency--who carries around that much cash?

If I have amounts less than $50 or so, and if it's a country that I know I will be returning to (my business travel tends to send me to the same places year after year), I just keep it in ziploc bags in my "currencies of all nations" box at home until I go back.

If you can't do the hotel bill thing, and you don't want to get hosed on the exchange, consider selling it to a friend or colleague who might be traveling to that destination in the next few months. I've done this also. Everybody wins, except the rapacious currency exchange guy!