Re: going more than once
To answer the poster's actual question: no, there isn't anything you can do to keep an erection after ejaculation. Ultimately, however, as you continue to have sex, get older and become more skillful, experience new things and reach new levels of arousal, you may certainly find that every now and then this is something that just happens. If it does, great -- if not, don't worry about it.
Most sexual partners DO NOT expect this; no one is going to be disappointed to see that you are responding in a perfectly normal manner with regard to male physiology.
Caveat: Viagra CAN help reduce the time of a refractory period, though not guaranteed. Most docs probably wouldn't prescribe it for this purpose, yet a few docs are in the habit of tossing V to anyone who asks. Unless you truly NEED it, however -- I'd recommend against recreational use.