There's no way to install this seat without LATCH and use the 5-point internal harness.

Yes you can, according to the link you provided.

For use as a harnessed seat; for children at least 1 year old and from 22-65 lbs:

Lap/Shoulder Belt + Top Tether
Lap Belt + Top Tether
Lower Anchors + Top Tether (LATCH)

The one drawback to this seat is if you rear-face your under 2. There's no option for that with this product. You would have to forward-face a one year old, in a position which isn't idea.

So basically, to sum it up; If you want to use the CARES on the plane, wait until your child outgrows his or her infant bucket, while should put them at the minimum CARES limit. Then switch to this product if you need a car seat at your destination and you don't want to use your normal car seat or use it on board.

It's not a complete replacement for a more traditionally designed car seat but a good alternative for families who travel a lot and those like yours' who live in big cities and don't really do a car that often.