(You need to Login or Register to view media files and links) ( just search for "epoxy stick" on the Home Depot site - that brings up 3 or 4 varieties)
this would likely work well, and not cost a lot. two part epoxy putty stick - this one (if the link works) is Loctite brand - I've used similar product on my royalex boat, to sorta make a sorta skidplate and lug a few of the deeper dings. easy to work, and since its a putty, would be easy to plug up the holes if you have something for a backing to keep it in place till it cures. the stuff I used, I don't think I even cleaned the hull, just plastered it on - and its still there after maybe 5 years of use.
Home depot has other similar products that are designed to work with plastic - "plumber's epoxy" stuff that isn't affected by water
the only downside to the epoxy putty, at least the one I used, is it dries white - so wouldn't look very pretty, maybe
most likely, any two part epoxy would work, but liquid versions would be harder to use to fill a hole, I'd think.
plastic welding ? maybe, but that depends on how thick the materail is - only experience I've had was wleding cracks in snowmobile gas tanks - using a soldering iron, and plastic coffee can lids - works, but you needed to have enough material thickness to melt a groove at the crack that could take the melted plastic filler.
G-Flex epoxy is another product designed for use on plastic and works for boats - not sure how much it costs and what quantities you can buy in (i.e. small amounts) - its also a liquid, so harder to use as a filler in a hole.
I'd think, even contact cement would do - just put a plastic - plate over both sides of the hole