(Sorry for some late responses, just tuned in to the thread...)
I thought the reason they added the rubber sleeve to the throttle return spring was to keep it from chafing on the bowl vent hoses running to the carbs..?
Anyway, even after the throttle friction adjusters were dropped, there is still a raised circle on the bottom control pod casting, so you could easily drill a hole in it and tap it.
For anyone who needs the parts (Mainly Junkie in particular), here they are (I just ordered 'em from a dealer, so they are available...):
Adjuster (the little steel "brake shoe" that rides against the throttle sleeve)- 53163-300-020
Spring- 53191-300-000
Adjuster Bolt- 53190-300-000
Here's a pic of the whole mess: