Strategy for backup for databases with little use (almost archived databases)
This (the full backup) generates a large backup set that, for various reasons I am finding it hard to deal with.


As you said you are not using compression I believe you can get good relief when you use backup compression. Just forget about the CPU utilization I have used backup compression many a times and the CPU utilization is just 5-10 % more in extreme cases. I suggest you to use it but before that read The Documentation


  I am looking for a back strategy that would not result in unnecessary backup size.


The backup strategy is to make sure you have valid backup when needed and using that you can loose as less data as possible, there is hardly a strategy for making backup size less unless you use data compression or backup compression.


  Is there a way to take advantage of the fact that inactives are simple recovery to threat them differently?


Backup size as such is not influenced by much by recovery model it determines the amount of data loss you can have in case disaster strikes.

Moral: Use backup compression it might solve all your queries.