The title says it all- how doi jump high without sif?
Rolling hops, my man. Use your core and leg strength to lift your legs up and bend your torso sort of in half, like you’re trying to sit in the air. That’ll bring your unicycle up higher than simply trying to lift your unicycle vertically.
Good rolling hops require a good amount of forward momentum, so keep that in mind.
Ideally you want to be able to SIF hop as well as rolling hop. Practice both and you’ll master them eventually. 
Yeah, rolling is the way to go. If you’re into trials though, try pre-hopping. That is, taking one giant bounce before you jump. Jam your tire into the ground so it compresses and springs you where you’re jumping.
And practice a lot!
Good luck!!
<3
There’s a Ryan Atkins (?) Jump High Tutorial floating around somewhere I believe…