I don't really know of any "two way" CB type thingys. you would probably need two of these
http://www.darvex.com/miva/merchant.mvc?Screen=PROD&Product_Code=SCB135&Product_Count=1
(proper rating of course)
Couple those with a 0 ga T block (1 0ga in, 2 0 ga out) and then run your 4ga off of each CB to the amp(s).
As far as using a CB as a switch, should be no problem, I do it all the time and the CBs I do it on are nothing special. Like you said, you are not planning on using it as a switch so no biggie.
What I am not sure about is, if a CB pops at its rating or a percentage above, like a fuse does.