You squawk 7700 but have no idea if your transponder is working either.
The transponder antenna,
AFAIK, is normally mounted at the belly, while COM is normally mounted on top. So I would assume that my transponder would be working. Also, if you see the R light up, it's receiving an interrogation signal to which it's responding. So the odds are all in your favour.
You have no way to talk to ATC
COM2, Icom, cellphone
a. Land at the controlled airport unannounced
If the fuel leak is so bad and uncontrolled that you have no choice, then it's a matter of finding a suitable flat spot and hope for the best. But if there's still juice in the tanks (and flying cross-controlled may well be a good idea in a 152) you've got time.
Controlled airports have mostly ILS or similar straight-in approaches starting 6+ miles out. So you can join a circuit relatively safely, start circling on downwind with all the lights flashing, and hope you get light signals from the tower.
Also, most commercial traffic on a straight-in approach will fly relatively slowly (at least not doing 250+ knots), on the extended centerline and display all their landing lights so from downwind you can see them and time your arrival pretty well. In fact, you could slot in between Mr. Boeing and Mr. Airbus and they'd never know you're there. As long as you manage to avoid their wake turbulence, that is. But there are tricks for that (three whites for instance).
I wonder what the legal (FAA or European equivalent) implications would be if you made a landing like that and nobody got hurt?
Pretty sure: none. Sure, you're going to have to talk to several people, maybe write a good report on what happened and why you did what you did, but if you can convince the authorities that what you did was, in your eyes, the best cause of action, then you've got nothing to worry about.