Ok, a few possibilities come to mind. You could make a pigtail with an eye in each end. If that would be too long, you could use the double-loop in it's figure-8 form. Or, consider the loop below. I made it by creating an eye and then burying each tail back into the loop (instead of one into the other). You don't need this splice to run through a block, so its bulk isn't a problem. 3mm Samson Amsteel Blue (Dyneema SK-75) has a minimum breaking strength of 1000kg. Even doubled back on itself (let's guess 75% strength) and taking a 50% safety margin, it should be up to the task. If you're worried, go with 5mm, which is more than twice as strong.

Regards,
Eric