Is there another way to do it?
FWIW the cue slips in my grip hand on almost every stroke I take, sometimes just a little, sometimes a whole lot. I make no attempt to do this, it's just a natural consequence of a very loose and supple grip plus the slick Irish linen wrap on my cue. If I try to "grip it and rip it" I will throw the cue off line so much it's alarming.
I also play around a lot with a true slip stroke. I used to think my grip hand moved back just an small amount, but after videotaping a practice session I saw that the hand usually slides back 4-6" along the grip. That's with a starting position well forward of my normal grip (almost at the front of the grip at times), but finishing with the forearm perpendicular to the cue. I believe this is more natural to do on a very forward weighted cue like mine than it is on a rear-weighted cue.
At any rate, I don't think either type of stroke is possible to do with a firm starting grip, particularly the slip stroke.
BTW I much prefer your term "release stroke". Even though I don't consciously release the cue, calling it a "stroke slip" has caused more confusion than it has eliminated.