I think Grip can do what you want. Ripping your flac collection as -q3 ogg won't take up much room at all, relative to the flac file size. Maybe 10% of your existing collection size.

http://www.nostatic.org/grip/

Foobar will do it under windoze:

http://www.foobar2000.org/

Not to mention you'll easily be able to fit a bunch of -q3 ogg files onto your NIT's SD card for when you're on the go.