Yes, they are exactly like those you've shown, only they're circular
in shape, allowing for simple(r) mortising with a forstner bit.

I'm assuming you've seen the router bits that let you do the same
thing without separate hardware? Such as:
http://www.leevalley.com/wood/page.a...168,46176&ap=1
If that won't work, I remember seeing a "shop tip" somewhere (a mag?
here? online? can't recall...) that basically used a fender washer to
accomplish the purpose you describe. That alone might work if you're
mounting on a screw or something with a larger head (i.e. not a finish
nail), or you could file/mill a slot on the inside rim of the washer
to make a keyhole slot. Either way, you'd just need to drill out a
clearance hole, then a shallow countersink for the washer, and you're
set.
It makes sense in my head - let me know if you want me to try to
explain it in more detail.
Good luck,
Andy