I have a NE Dory. From what I imagine based on your description, it should work.  The hull is flared outward significantly at the point where the oarlocks are located, so your design will need to account for that angle to bring the top of the lock up higher than the gunwale. I imagine you welding up something like a a capital "A" with the lock at the apex, with the two legs of the "A" bolted just below the outer side of the gunwale, and adding another leg that will touch down a little lower on the hull. Not too low, expecially if you'll be using the boat for sailing, to prevent dragging in water when healed. I'm unsure of the typical distance between oarlocks on a sliding seat/dedicated rowing rirg, but do presume you only need to add something that will move the lock out something less than about 8 inches.  I'd get the oarlock designed and built prior to finishing your build, and then use it so you know where to add in a few pieces of plywood plate to strenghten the places where your lock base will attach (screwed to or bolted through) the hull. Bolt-on would allow easier removal, if you plan on taking the extended locks on/off. Maybe 1/4 okume, probably on the inside of the hull to keep the outside looking fair/nice. A little piece of tape would probably be suffient to cover the lower hole when/if the lock isn't in place.

The whole contraption could probably be made of wood if you desire, one horizontal triangle facing out with the lock at the apex, with another triangle support oriented vertically (like a shelf support) underneath that.

If you can find an aircraft mechanic (or someone else) capable of welding aluminum tubing, you could get really fancy and light (and costly, I presume).  Getting the lock itself, or the lock insert, set up on the end of the rig might be another engineering challenge.

Just had another thought: maybe you can salvage the ends of a "wing" rowing rig, and start with that as the beginning for your lock contraption.

Or maybe this leads all the way back to making an acutal pre-build wing rig fit into the boat...

And I didn't know what a Concept 2 oarlock was, so just looked on the internet and came across this interesting picture of a wooden wing set up, which might leat in a whole 'nother direction. https://angusrowboats.com/products/carbon-fiber-rowing-seat 

Or, you may have something totally different in mind. Plenty to think about, which is much of the fun. - Bubblehead