Thanks Reedwalker. I actually saw a plumber in a van a couple days ago and asked him through the car window... recommended a hacksaw. I figured tinsnips might work, but wasn't sure.
I'd install a bleeder 90 if this was a typical installation, but it's not. The supply starts in the bathroom with a small 3' BB, 90's back into the wall and remains @ BB level until it 90's out the rear bedroom wall, where it enters the bedroom BB, right through the bearing wall into the livingroom BB, 90's for another 6' of BB then 90's down under the slab to avoid the entry doorway. After passing the doorway it 90's back up to BB height, 90's into the BB and remains that level until it reaches the boiler. So I think the smart thing is the 90 in the livingroom where there will always be that pocket of trapped water in the pipe in the slab.
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[ bedroom wall bearing wall livingroom wall ]
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[ 90's down into slab ------> 0
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[ <--bath BB
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[
[
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[ 90's up into kit BB -> O
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o<---up and over ceiling to boiler behind kitchen (--->) ] <- into boiler zone valve
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