I would try a large diameter, short brass nut, washers and bolt into a tight
fitting hole with a "suitable-for-fuel rubber" washer each side - then drill
and tap the brass bolt and screw in the (or a new) petrol tap.
This assumes you can get a nut into the right position and it will self hold
whilst tightening up ( use loctite ).

If not, and this assumes the plastic is thick enough, drill and tap a larger
hole and either fit a petrol tap in direct, or a bolt which you can then
drill and tap perhaps with a washer on the outside to strain relieve a bit.

Or as the others suggest - get a new or s/hand one but then thats not
D-I-Y...

Also depends on "what if it leaks" - a lawn mower/ outboard motor I wouldn't
worry so much, but if it leaks somewhere where vapours could collect, go the
new route.

Nick