Well, you might not like my method, but it works...
I start with a scrap of steel that is going to become my insert toolholder. I machine all surfaces as needed. The top is machined so that when the insert is layed on it, the insert will be at center height - don't make a pocket, just make the top flat. Now position the insert and use a transfer punch to mark the center hole. Drill and tap the hole. Mount the insert, oriented the correct way....yeah I know...there's no pocket...just be patient...
Now go get a little piece of steel. Depending on the size of the insert, but I often use a short piece of 1/4" keystock. Butt it up against the insert. Clamp down. A quick tack with the MIG and remove the insert (don't want much heat in that carbide!). Now finish welding. Grind, smooth, etc. accordingley.
Mount the insert again and scribe along the edges so you know where you need to mill off the extra toolholder for clearences (picture a round insert or triangle insert mounted on the end of a rectangle....you're going to need to remove material...).
I know it won't end up winning any beauty awards, but it works!
Andrew