I don´t know, if the Carthaginians can handle the culture penalty of the Ptoleys, but if you want to keep them alive, and, at the same time, weaken the Ptoleys, why don´t you invade Egypt, and give those settlements to the Carthies, so they can make a fresh start? :)
It would be a super D-Day, i guess, but this way you can grab those worthless desert settlements from the Carthies and let them rebel, to keep a buffer zone between their new and former home.