The movie was "My Boyfriend's Back" (1993).
The actor who uttered the line was Matthew Fox, now known from the
television show "Lost."
I ran the quote through a newspaper database available through my
local public libray and came up with:
'It's time to take another look at 1993's "My Boyfriend's Back," a
comedy about a teenager who dies, and then crawls out of his grave to
take his dream date to the prom.
...Matthew Fox of "Party of Five" looks very clean-cut as the dead
guy's rival, Buck Van Patten. Fox wears tennis sweaters and a
letterman's jacket, and woos his steady by saying things like, "I
would walk on glass and eat donkeys for you."'
source: Chicago Sun-Times, June 8, 1998, page 33
A "Lost" fan also mentioned the quote last year on a messageboard
devoted to that show:
"... i also like how he said he would eat donkeys for her.. how random
source: Lost Forum, 4/26/205
newspaper database: "eat donkeys for you"
google: "boyfriend's back" "eat donkeys"
I hope this helps.