I agree with Cedric on these points. I have setup my Golem BOV to be connected to my onboard diluent. I have my setup similar to the pic below and it works great. No extra plumbing or QC or whatever.
Y Block & BOV 1.JPG
I agree with Cedric's second point on having a 2nd stage available on each sling tank you have. It is simple and makes sense. Like Heavy Breather says, "O/C is for bailout".