I have considered doing this actually. Hard to tell what USB cables are quality or just the same garbage you already have.
What are you using now if not risers? Onda boards? Sell me one? hehe
These are the ones I always used:
http://[Suspicious link removed]/2BMxYAt
They aren't the cheapest, but they're not bad and super reliable - I don't think I had a single one not work. For my last build 3ft was the ideal length, but they sell smaller ones that might be better for most people.
I've tried all those - Colorful, Onda, etc... TBH I love them all, you really can't go wrong with any of them, even some of the weaker ones.
I actually did buy and try to use these. It gave me all sorts of issues where the video card wouldn't even show up at all, and some would. The ones that did, when I went to go mine, it would lock up the system. I switched to the shorter included mintcell cables and it solved those problems.
I also found a website that shows where longer USB cables puts strain on the system itself killing speeds it can transfer and that 1.5ft was pretty much the longest you could use.
So I am curious as to how you got 3ft to work reliably.