Drilling and tapping will do far less harm than welding something to it.
Tell you what, find a part on the frame you don't mind scratching, if you can dig your pocket knife or a file into it, you can drill and tap it. Worst that could happen is you will break off a drill bit or tap, the stuff is hard and requires great care.
The metal can be machined using the same equipment and via the same processes as stainless steel.
Pure titanium is quite ductile, but bike frames are full of alloys, test it first.

If you are not good at this, I suggest a Machinist, a good OLD mechanic who drills and taps a lot.
I am also a Gun Smith and have no fear of drilling or tapping unless it's stainless or titanium, that stuff is ruthless. It can be done, with the greatest care.

In fact Titanium has the benefits of stainless but without the weight.

http://en.wikipedia.org/wiki/Titanium

I hope this helps, no superstition, just a guy who has broken a lot of drills and taps.
You do have other options.