Another *** for the idea that a sporran with trousers is just wrong and weird. If you have to go that route, wear a fanny pack.

However, I've considered wearing a tweed Argyll jacket with trousers (slacks or khakis, not jeans). To most folks, it would just be an interestingly-cut jacket. Even though it's wrong*, it still wouldn't look as wrong as a sporran with trousers. When a sporran is taken out of the kilt context, it would just be a bizarre crotch-mounted man purse**.

*It wouldn't be wrong with tartan trousers/trews.

**Sporrans were historically worn with the old-style trews which were more like tartan tights, as seen below.