You can't easily put shutoff valves anywhere in
oil plumbing, since it's a loop. (Also consider that if you use two valves, putting them in mismatched positions would block
oil flow and be disastrous.) I've never seen a Y valve in AN plumbing, although one might exist. In any case, shutting off the entire long loop to the cooler would be preferable for several reasons. You would probably want some seep pressure through the cooler and lines to keep the
oil from sludging up in there.
Thought RB's way: that's a nice emergency piece. I was looking a AN part prices and found it would be cheaper to use AN-NPT unions and a section of iron pipe. Nowhere near as pretty or sexy, but certainly functional and a good "get-her-home" part.