There are a few products out there to add one to your BX but not cheap, or you can buy a bolt on thumb and like Garyoc posted above and then fabricate a mount for it on your FEL, then figure out how to add a third hydraulic circuit to your FEL to control it. Do a search in the attachments forum for "grappleomatic". Member Artisan posted a very comprehensive thread on how he added one to his BX25 and I think there's links to other products/options in that thread.
The thing with a grapple on a sub compact is knowing your limitation. For lifting brush you would probably be ok, but like MessickFarmEqu said, you're only going to be able to lift 200-250 .lbs. So you might have some problems if you are going to lift cut logs.
That being said, I still want one on my Sc2400. I made some brush forks for my Sc2400 which work good, but I'd still like the capability of a full grapple.
The weight of the bucket for the Sc2400 is 130 .lbs. The weight of the smallest 38" grapple from WRLong, is 280 .lbs. Bolt on is 143 .lbs RBG