I definitely wouldn't say "impossible" but with lovebirds it can be sometimes harder to get two to bond than many other species. As long as you go into it as you said knowing they may never get along and having two separate cages there shouldn't be any problem. If you are having high hopes of them getting along and caging them together then I would say it would be better not to try.

We have had lovebirds that were single birds in a past home that seemed to do better with a companion but we have had some lovebirds come into the rescue because when introduced to a second bird they either did kill the other bird or tried to kill it. If you do decide to introduce them later in hopes of housing together do so very carefully and with lots of supervision. NEVER just stick them in a cage together and hope for the best or you will most likely either end up with an injured or dead bird/s.

Good luck whatever your decision.