If you decide not to wait for the reamer, you have at least a couple options. The first is as you described; i.e. find out from your smith exactly where he wants the bullets to be seated. Different folks have had found quite different optimal seating depths for the 90 VLDs based on their specific rifles. I'm seating them at ~.018" off the lands. There are one or two others that have also found a similar optimal seating depth. At the other end of the spectrum, some people have found that about .010" into the lands works best. Because you do not yet know where your rifle will want them seated, my guess is that your smith might want the dummy rounds seated at approximately "touching", but I don't know that for sure. You won't be able to send him dummy rounds with the bullet seated optimally because you don't yet know where that depth is. The difference between the two extremes I listed above is almost .030", which is likely much more of a range than the smith is going to want to determine how to cut the throat. Let him tell you where the dummy rounds should be seated.
Alternatively, Kiff (PTG) may have one of their UniThroater hand throating tools currently in stock. You can call and find out. If your smith doesn't already have one, you could get one pretty quickly if they're in stock at PTG. With this tool, your smith (or you) can easily lengthen the freebore of a chamber cut with some other .223 Rem reamer to whatever you want. If you go this route, just be very conservative with the tool. It doesn't take much to remove the tiny amount of metal in the throat area and you don't want to lengthen the freebore too much. Other than being cautious when cutting, the tool works very, very well. For this approach, your smith need only use whatever .223 reamer he may already have that is appropriate, then lengthen the freebore with the UniThroater tool.
If you haven't already hooked up with one of the previous posters in this thread, send me a PM. I already have dummy rounds loaded for my rifle at ~.020" off the lands, which is as far as you'd really need to go in all likelihood, and at "touching". I could send these to you if they would be helpful. I'm in the process of packing/moving, so let me know if you're interested, send me your contact/shipping info, and I'll plan a trip to the Post Office next time I go out.
Just be aware that CBTO measurements of dummy rounds made by someone else will likely not be the same with your specific calipers/insert. I don't think the smith will care, but don't freak out if your measurements don't exactly match those made by whoever sends you the dummy rounds. Simply measure CBTO and COAL for the dummy rounds you're going to send to the smith with your own calipers and record the data, prior to sending them off.
Finally, with the 223 Rem ISSF reamer (0.169" freebore), bullets seated at .015" to .020" off the lands have the boattail/bearing surface junction very close to the neck/shoulder junction. It is just ever so slightly above. Really, you don't want [need] to go any farther off the lands than that. If anything, there is plenty of neck to move the shank farther out, so I'd be looking in that direction, definitely not any shorter. At the other end, maybe .010" into the lands is about as far as most people jamming them have found to be necessary. So you have an overall seating depth range of about .030". For that reason, it is probably not necessary to go through the VLD seating process from Berger outlined by Phil above. It's a great approach if you don't know where you'll be and has worked well for a number of folks. However, in this case you have some pretty solid information about the seating depth range successfully used by a number of shooters with the 90 VLD, so I'd start there first and possibly save yourself some time/effort. I have attached the print for the ISSF reamer below in case in might be helpful for you and/or your smith. Best of luck.
