Yes, it is. You can even board and then de-board, and get a refund.

Fully refundable ticket. No fuss, no muss. No one should have to beg Delta or any other entity to go airside whenever they see fit.

A gate pass would be the way to go. I have done this many times and it is really no big deal as long as you have a decent reason. Best thing to do though is to plain a little extra time to take care of this at the airport so that you are not in a hurried mode. It also helps if you have detailed flight information.

I'd do WN, too.

Can cancel it from your phone while you sit on the train heading to the gate.

I did NOT have a good experience trying to acquire a gate pass for Terminal E in Logan. My wife and two young daughters (1 and 2.5) were flying Lufthansa to Germany and I wanted to be able to help her through security, etc. I called the BCP, TSA, and Lufthansa. Each of them stated I would need to request the gate pass from one of the others. I started this 3 weeks in advance and I never did get a gate pass.

So...

YMMV.

--Mike

I think a gate pass will be a much easier solution here. But your plan should work too. Like others suggested, book on WN if you really want to go that route.