Yes any *A J/F pax can access a Polaris lounge.

Here’s the way to do it. Check in with AI in Terminal B. Then take the AirTrain to Terminal C. Once in C - you will have to clear security to access the Polaris lounge. Tell TSA you’re visiting the lounge and they will let you through no problem.

After you’re done lounging, take the shuttle from C Gate 70 or so (I think) to B. I’ve forgotten which section of B the shuttle drops you off at (it’s probably B2). You might have to clear security again to reach the AI gate (B3). Of course if you need to clear security at B - taking the AirTrain would be the same. You can also go to the LH or SAS lounges in B - but they’re no where near as good as Polaris and you’ll have to clear security twice as well (perhaps shorter lines though).