Just because the lil ones are staying home with the sitter, doesn't mean they aren't entitled to a celebration. Have some party hats and noisemakers available (or materials for them to make some) and get them in on the action.
Bugbee also recommends, "Allow the sitter to let them experience New Year's Eve before midnight by watching another time zone celebrate (London or New York, depending on where your'e located) on the Internet. The more you offer the sitter, the more fun she'll have with the kids. And let her own some surprises, even if you've planned them. "