I think you can but you're going to have to let out sections of line to see how it reacts. Maybe let out 10 feet at a time and see what happens. Even the floating line will be tapered for up to 20 feet. Or you might have sinking line on one where only a certain length at the end will actually sink.
Sounds like a pain in the arse but definitely worth the try. Pretty pricey to have to replace a good fly line.
Better yet, sneak away and test them by throwing a nymph at some bows in the river.