OK a few small ideas for involving the crowd but I don't busk...so all untried from my part execution is on you:
Letting one of them hold the non-dominant stick in 2D/3D (easy examples of this on YT)
Letting them hold the top stick while you elevator
Shuffles, orbits etc around them
Landing some sort of stall on them
Letting them hold a grind/gyrogrind/stall already landed
If you can pull it nice and high then highthrow - front/sideflip over someone (easier version to jump over them normally or maybe roll over back) - catch
If you got good splits then go down in 1D - mach 5 variation and then "pelviscrawl" your way through participants legs nohanded
^Variation cause I can't find a reference vid to explain "pelviscrawl"...use 2D neckstall, place sticks in mouth and use your hands to crawl through
Magic knot with just string (loop in another loop got it on my YT from like ages ago for reference), let them blow on it to untangle...supereasy
If you've got a good, smooth surface (maybe wood you can place out?) then gyro - floorpass to yourself through participants legs (aim prolly difficult)
Jokes...since you've got bagpipe playing friends maybe make them the punchline of every single one

Have someone hold one of your sticks, throw diab in the air, grab stick from them and immediately give them back the other one (without them expecting ofc), miss the catch, scold them for fumbling
Use audiences heads for diaboloshelves...also keeps the "victims" from walking away during. Maybe try to make them catch something in the cups (throw something soft) or with diabs on their heads pit them against eachother gladiatorstyle.