Amazing how common sense often flies out the window when anything to do with sex is involved...
A couple of years ago I met a guy in the UK who I had corresponded with on various sites - he is another tight jeans freak. He was REALLY keen to meet me, and I think he was trying to "prepare for the event" bu wearing a kind of band around the bases of his cock to work like a cock ring and keep it hard. To me it looked much like a rubber band.
The effect it seemed to have, though, was that it kept his dick semi-hard, then when the time came for us to do a bit of mutual stroking it was reluctant to get any harder. This was the case even after he remomoved the ring thing. It was as though no blood was leaving the thing but no more was coming in either.
We had a good time anyway, but I really wanted to say to him "For goodness sake, you didn't need to try and pump yourself up for my benefit, I don't judge people by their dicks."
I'd imagine that leaving any tight fitting ring on for any length of time would be a bad idea, especially an elastic one that maintains the constriction even after the dick shrinks. There is a condition called priapism which is basically an erection that won't go down. While this might sound funny or even appealing, it is in fact highly dangerous, since it can lead to impotence, which is kind of the exact opposite of what you were looking for.