Toilets, Sinks, Showers, Tubs and Disposals - basement shower remodel question

I just gutted a basement bathroom to the studs. Shower was a tile shower 36x36 that was falling apart. shower floor is cement, the problem is we want to put a fiberglass shower unit in but the old drain isn't centered. From side to side it's centered at 18 inches, but it's 24 inches from the back wall. I'm thinking about building up the floor where the shower will sit and have a six inch pipe from the shower drain go into the existing drain. Is this a stupid idea? I really don't want to break up the cement floor if I don't have to. Any sugestions?

If you do not wish to chop concrete, this is the best idea. I have seen many showers built up this way and a drainline run over to a floor drain. Good luck with your project.