Having been there - if you can't EASILY get it to come out with a good set of vice grips, I'd take it to someone unless you've had experience working with this stuff.
Drilling: Definitely don't try and drill it without a drill press like
@Billy Goat Suggested. Freehand it's too easy for the bit to "walk" and you want to start small, center it, so it leaves you metal for an extractor to "bite" into. And, you want to be able to re-drill progressively larger if needed without touching the riser.
The tig weld a nut trick does work, and it is probably the best/easiest option (for someone with the tools/skill), because you can size up the nut to go over damaged threads, or run a die over them, and you have a lot of control over the amperage and heat you put into the metal. (And, that heat and metal expansion often helps free stuff ip) But, you need someone with the gear and knows what they're doing so they don't overheat things. I've had that work when drilling / extractors / etc failed, but then again I have a Tig Welder, drill press, band saw, etc downstairs...