This is a cool thread. I've been reluctant to add something as there are so many more seasoned guys who have already contributed ....
What's really interesting is to see what techniques and tools others have developed and/or adopted and modified over time to suit their needs and to find out that what I've come up with ain't too far off.
I abandoned the flat graver as an undercutting tool when I kept trashing the opposite side of the inlay channel ... especially when inlaying wire under 1/4 millimeter.
I made a miniature, offset, flat tipped graver that allows you to get lower without trashing the opposite side of the channel. Since this photo was taken, I've modified the tools taper from 20 degrees to 15. The sides are tapered at roughly 25. Once it is a razor sharp, narrow, flat tip, I knock off the point on the porcelain wheel to eliminate the probability of tip breakage while facilitating the tool's ability to push material. It's still sharp enough to raise teeth along the bottom of a very narrow channel too.
Also, I find that an ultra tiny burr along the edge of the channel can be helpful when shaving off the excess. Gold shaves (or tears/peels) away at those points without having to dig in and possibly nick the surrounding steel. One of these days I'll get around to making a flat graver out of brass for scraping. I know sometimes the luxury to stone back heavily to eliminate it is not available .... but then again, a deeper undercut, which raises more metal, keeps the gold in place in the tiny tapers. After reading this thread, I figure I'm over-engineering things as I always do ... but I've accepted the fact that I'll never be a "fast" engraver because of it so I guess it's ok