It's possible, did that already actually but this is not in FIMK atm.
The reason for the absurdly low number of blocks might seem arbitrary, which it actually is, since its simply the biggest number you could fit in a 2 byte SHORT.
The database uses a SHORT field to store the balance lease period which gives us the weird small number.
Why is it not possible to lease ones balance for more than 32767 blocks? How was that number determined?What if forging hubs don't include transactions (that would take their forging power away) into the blocks?
Maybe I am missing something but wouldn't it make sense to be able to lease indefinitely and have a new transaction sub type "stop leasing"?
To answer that question: "Simple, the next the forger will include that transaction in a block".
The answer about the plugin could work, albeit that the NXT plugin system is very overrated (as is everything client related to NXT) and it would of course never work for your headless server nicely tucked away on some server you never touch.
The real solution is to change the balance lease field in the database from a short to an int and you could lease for millions of blocks.