Here's a couple of ideas that I used on all 3 of my ST and both of my FJRs. Pictures are of my FJR, but the ideas are applicable.
First, you can get RAM mounts that replace the back brackets (on the handlebars just inside of the grips) that hold your clutch and brake assemblies in place. It's a solid mount and you can put whatever you want on the RAM balls.
Here's looking from the left side.
Here's looking from the right side. On my FJRs I needed the supplied spacers, I don't recall needing them on any of my STs but they come in the RAM kit in any case.
(Also, I just noticed, you can see a mounting plate on the brake reservoir, discussed next.)
Inexpensive as well.
Second, you can cut mounting plates out of something easy to work with (mine are some kind of hard plastic I got at ACE hardware). Cut to shape as needed for whatever you want to put on them. Drill holes to match the bolt locations on top of your brake and/or clutch fluid reservoirs and replace the two mounting bolts with ones a bit longer to account for the thickness of whatever material you make the mounting plates out of. Bolt them on. The first set I made, I was real detail oriented and tapered the bolt holes for flush mounting, but . . . didn't do that this time as I had these bolts on hand using them saved a trip back to ACE. The bolt heads aren't in the way, so . . . maybe I'll get around to redoing it in the future. Yeah, sure!
Any questions, let me know.
Both these ideas provide solid mounting points. Have fun farkling!
Shuey