I remember that in the old thread it was mentionned that the current premade queue does not allow to sign up in group of less than 6, does it ?
If it would (that is : if premade queue worked like the old mini queue) it would be less of a hassle to get some of those games going ?
Also if premade queue was made more visible and not look like a hidden feature as it is now, it may help, I think. So that the info that there is some premade about to happen will be available to players who don't actively search for it (but wouldn't mind participating).
I would start with that and see how it goes before adding additional rewards or implementing server based rulesets.