Good luck with this.
Think about this:
If you transfer at your 48-52 mo window you will most likely be a senior 2nd or new 1st class, and most likely either qualified EWS/PPWS and a knowledgeable and needed member of M-Div. Right?
Then you go to ELT school and now you are a heavy Mechanic and a Nub ELT so where do you go?
If you go to Proto, you will be a useless ELT no better than a ELT MM3 straight out of Proto quals. What role would you expect to fill at Proto as a Sea Returnee "ELT". You could serve a function as an M-Div body, but you are not a Mech anymore, you are a 3356/86 and are now expected to be an ELT. As a senior MM2(SS) or junior MM1(SS) you would be expected to serve in a position of leadership in RL-DIV and you just by circumstance could not.
Radcon is a possibility, since they send all ratings there for that NNSY Radcon school...
IMHO if you take the ELT re-tread route, the best thing to do, would be to return to sea and learn to be an ELT at sea.
Since the Navy is so short right now on ELTs, I bet you will be heading to sea as an ELT sooner than later.
I really cannot think of a way you would serve as an ELT in a shore capacity after finishing ELT school. You would just not have the sea-returnee experience expected of you as an ELT.
Unless, between now and then, you "qualify" as an "ELT" at your command by studying and performing prac-facs under the supervision of the LELT, document all your OJT, take some qualification exams as an ELT would, and then put it all together in a package signed off by your CO, documenting your ability to serve as an ELT on shore.