Sounds a neat trick, i’ll give it a go when I get home. Another one for the list of tricks, although its fairly commonly mentioned is to (away from the rim) turn the tyre inside out and leave it for a while. Then when you turn it the back again the bead should want to push out more and help seal against the side of the rim when you mount it. If the tyre has a wire bead, which most uni tyres probably do, be careful you don’t snap the wire, its quite easy to do.
This is how I’ve done mine if it’s playing silly buggers. It also has the handy side-effect of showing where any holes or porous bits of sidewall are with all the bubbles… 
Yeh I love the bubbles too 
If theres bubbles coming out you can give the tyre a squeeze in that area to try and get a better seal.
Don’t you end up with loads of washing up liquid mixed in with the sealant? I would imagine that wouldn’t help its sealing qualities…
Rob
I’ve not had an issue with washing up liquid but it did not help create the required seal when I converted my tyre to tubeless (the third tyre I’ve converted).
The problem was that the tyre was quite loose on the rim, much looser than the pervious tyres I had made tubeless. So I wound 3 layers of waterproof tape around the rim, giving the rim a larger diameter. The tyre now had a very tight fit and hence sealed and inflated very easily using a track pump alone. I also believe that as the tyre is such a tight fit to the rim the chances of burping are reduced simply because the tyre has no room to move on the rim.
Jamie