...but I'm not at all sure it will work with ABS...
I am certain. Normal epoxy does not bond to ABS.
Well - when I think of epoxy - I think JB Weld. That said, I have the cover of an old battery from a Motorola "brick" phone that I use occasionally for mixing epoxy; I can bend it and pop the epoxy off (mostly). Not sure if it was made of ABS or not...?
With an interesting exception: openings in the ABS give the epoxy a "bonding" point. I have had success "gluing" tactile pushbuttons into openings. The epoxy forms around the opening edges holding the pushbutton in place.
One thing I had done to get some of the epoxy off that battery cover was to use a hammer and chisel it off; but I found the epoxy would stick better the next time around (perhaps the gouges were making it easier to "stick"). So you could probably just sandpaper it some to make it stick. Worth trying out, at least.
I've found JB Weld to be good for sticking together just about anything; my "worst" application was on an anti-backfire valve on my 79 Bronco. That valve is virtually impossible to find, and the one that I did find (off a junker engine) was broken. I JB Weld'ed that thing up, and it's been on that exhaust header for several years now, without failing.
I've also seen JB Weld hold together a blower on a diesel engine, on my brother-in-law's old Ford dump truck; the blower cover was an aluminium casting, and had cracked. My brother-in-law had no way to weld the aluminium, so he JB Weld'ed the crack. It held for over a decade, then the blower failed again. That's when I first saw it. It had cracked in a -different- spot; he told me about using JB Weld on it the first time, and showed me the repair he had made before; it was still holding fine. Of course, after the second crack occurred, he decided to get a replacement blower.
All anecdotes, of course - and says nothing about ABS.
Gorilla Glue (or another polyurethane-based glue) might be another possibility. Something else to try might be to get some ABS solvent (ABS pipe "glue") and take a little bit of it and mix in some ABS shavings to make a "plastic blob", then embed the standoff into the blob onto the ABS piece you are working with (probably a metal hex standoff would work best - basically, the idea would be the inside threaded end of the standoff would secure it longitudinally, while the hex part being embedded would keep it from rotating - but that's all just a guess).