What helps is to pull out right at the PONR and squeeze the base of your penis very tightly. It suppresses the orgasm somewhat. It takes practice though and I guarantee the first few times you try it, you will bust a full nut and not be able to keep going. But after a while, you learn just how much to "let go". Sometimes I can go three times in a row using this method...but going at least twice is a given. And I mean right after...no refractory period at all. Pull out, squeeze, cum, right back in.
Oh...and keep a towel and/or extra condoms (if you use them) handy.