For us there is a definite combination of two things. Me being able to let go and Mr LNT listening to me regarding positioning and pressure.
Gotta say I don't only find it very pleasurable but fascinating too.
We have just managed this recently. Only a couple of times so far but it has to be said both occasions were slightly different so I don't think the technique can be set in stone.
The first time it happened I had no clue what it was, just that it was amazing. I do find that when men are purley aiming for squirting in an intence way it will just be painful or uncomfortable for me. Best thing to do is take your time with it and dont force it. For me it hapens sometimes with a partner and always when i masturbate, would suggest you try playing alone to figure out what you like in that regard and if it happens when you use certain toys (I persoanally love a glass dildo and a small wand combo, the glass alone usually hits the right spot but the added vibe is a bonus) or possitions just take it slow and figure it out for yourself (even let the OH watch if that does it for you). That way you can properly instruct them when they try and you wont be so shocked or uncomfortable by the needing to pee sensation before it happens.
Glass dildo I love just an FIY