As susceptible as Catharanthus is to crown rot/wilt diseases (like Phytophthora), I would be very hesitant to try this. If it were me, I'd prune it back and take a bunch of tip and softwood stem cuttings for insurance. Then I'd give the original plant some half-strength liquid fertilizer. I'd tip prune, if needed, to shape it as it regrows
If it still looked leggy, then I would plant something like Fan Flower (Scaevola) around it.
The apricot varieties of Catharanthus are always my favorite. So pretty!