I used 3M "Extremely Strong" mounting tape - the kind with red plastic peel-off strip - with no screws or rivets when I added a Powerbronze Fender Extender to my Z900RS, and it seems to be holding perfectly so far. To be fair, it has only been a few days and a couple of hundred miles and no bad weather just yet. But I did the same with my Pyramid Plastics fender extender on my Versys 2 years and 8,000 miles ago, and it is still holding strong. I would also feel quite confident in using 3M Plastic and Emblem adhesive for this task, and would have done so if I'd had a tube of it handy, because it would have been slightly easier than cutting the tape to fit. I once used it for attaching vinyl trim to a car and it stuck like a barnacle. It held for years and is probably still holding today, if that car is still on the road.
No, I don't work for 3M or get anything for mentioning this, I just have tried and been very happy with these two products. YMMV.