You may be expecting too much...
With your (coming) vang, my suspicion is that you might find the traveler not as critical -- unless you determine that you somehow need to be able to pull the boom higher than centerline.
The typical setup on a DS is not that adjustable and mainly redirects the angle of pull to align with the stern quarter rather than some point on the centerline of the boat. Also, it reduces the length of doubled mainsheet a bit, but that's secondary.
Usually they are set up so that the boom ends up just a bit below centerline when tight, but closer than if you used center boom sheeting.(There's a rigging guild on the DSA main site -
https://daysailer.org that I've been following loosely).
However, if you want to mount a track on the transom: there are no class rules to get in your way, and perhaps such a setup fits your style better.
Some people have used split-tail mainsheet rigging, but if you do that, you don't get the 2:1 purchase at the end of the boom.
Out of curiosity: how is your boat rigged today? Simple center boom sheeting?