Bones.. and that damned hemd :D
I ended up adding short bones under the hook/eye tape on either side of the front opening. As a happy coincidence the tapes are almost exactly wide enough to hold the bones. So it was very easy to tuck them into place. The bones are about 7 inches long.. so 1-2 inches shorter than the hook/eye tape (I was using what I had on hand). I pushed them all the way to the bottom of the channel, stitched them into place and left the top 1-2 inches of the front opening un-boned. I like the way that worked out so I plan to continue to do that on my other German dresses.
Based on pictures from June Crown it looks like the bones are cutting down on the zig-zag of the front opening.
As a “bonus”, the night before the event I decided I didn’t like the way the collar of the hemd was looking. So I removed the fabric from the inside of the collar (Because really, there’s no better time to drastically alter your hemd collar than the night before an event). This made the collar easier to iron to get a nice crisp honeycomb showing up.. but also allowed the collar to stretch out to MUCH longer than is actually needed for the neck. I’m not pleased with that. The plan right now is to make a new hemd with a smaller collar and then possibly come back to this shirt and fiddle with it later. I don’t want to tear apart my only hemd in order to fix it.. and leave myself with no usable hemd. So I’ll work on a new one first.