Not sure which threads you should check now, besides the one cited already.
I have used an Aurora Solar Charger to charge my 5600 and it worked. I believe the C1000/3000, 6000 power is pinned out the same way, but am not 100% positive yet. But if they are there is no reason the Aurora won't work.
There are other products on (or coming) to market that look promising too. The more advanced ones will do a very good job of regulating current, but some of them also will not have adapters to charge a Z so you'll have to roll your own (I'm thinking of both Bruton and POE here).