Martin Potter:
I am wondering if anyone has had experience with any tantric or down-to-earth techniques on withholding orgasm.
Hard to do. Though easier after stream entry, it was all but impossible before. For me it requires high concentration & (very) high willpower

A lack of either means I'll loose interest (rare) or go all the way (frequent).
Didn't get much benefit from this otherwise enjoyable "practice," though I didn't put a lot of effort into it, to be honest. It turns out to be a meditation all in itself, and a quite laborious one.
For more on tantric sex / tantric wank-fest, you can check out the
AYP website.