Just zap the reply and then reply to it 😂 

 I can in Primal.  Respond to this and I will 

 I'm in Primal as well and I can't see how to do it 

 Press and hold down the lightning bolt on someone’s post and you can adjust the amount and comment.  

Here’s a little vid.  
https://m.primal.net/LGdm.mov 

 If the note's good enough to reply to, it's good enough for a small zap.

It's the boosts that should be zapped heartily though.

If you boost a note & don't zap it, who are you really boosting the note for?  

 With Primal, zap from their profile and the note option is available.