In theory this should work, we pump almost 14ft up to our feed tank and I would think with pumping concentrate you're less likely to freeze because of the heightened sugar content. Obviously making sure the line has slope is going to be a big deal because if it does freeze you'll have 1 or 2 issues...

1. The line will blow apart at the fittings

2. If the RO has a high pressure sensor it will just kick off and you don't be able to process the sap until the line is thawed.