What about being able to weight witness votes out of that top 7/21/30 whatever the magical number is. "I like this witness a lot, so I'll vote them with x vests." (Perhpas more than 1 vote, as it stands now) - I like this witness more than this other one, so it gets less vests.
That, or a preferential system, that then aligns your vote power in vests for that witness with your stake.
Vote 1 x for witness 45% of your vests
Vote 2x for witness 15% of your vests
Vote 4x for witness 2.5% of your vests
I'm to tired too work out the arithmetic, but I'm sure someone much smarter could work it out.
Maybe even a witness power slider bar that lets you adjust how many of your vests approve that person's witnessing activities...