Through the power of sense-sharing, I think that Loop should tie up Siffrin and watch him squirm and beg and come untouched from Loop masturbating in some form alone

Loop should make Siffrin masturbate in front of them as some kind of powerplay to have him pleasure Loop without being allowed to touch them.

Loop should cheekily suggest to Siffrin one day that he should get in a little masturbation session before he goes to sleep alone tonight so that Loop can feel it, and waits to see if he actually ends up doing it or not (he does, because he likes the thought of driving Loop crazy where he can't even see it)

And then there's Call sex where one of them describes over the line doing something to the other while they're doing it to themself to transfer over the sensation. There's many possibilities with sense-sharing, you see

Mid-loops Loop playing with their chest star at the tree and watching Siffrin suddenly go from deadly silent panther to stumbling his way through the House with flushed cheeks as they hurry their way to the bathroom for privacy because why does his chest feel on fire