Looks like a vacuum operated EGR valve?
You could cut the current nipple off flush with the main housing and carefully drill and tap it, so you can fit a screw in bleed nipple.
Something like this;
You'll need to be very careful though, because there will be diaphragm inside the casing and you won't want to get any crap / swarf inside that might puncture it. Also overall depth and wall depth - there might not be much thickness to the plastic that's available to have a thread cut.
And if you're fitting a metal nipple to a plastic housing, very easy to strip the thread out of the plastic...
Might be possible to glue a plastic nipple on, but that's normally not very strong.
