You might need to get creative and put a T fitting somewhere. Here is an example but your solution will have to be a different with hard tubing.
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If you are putting in a bottom rad (or rad with ports on bottom) that would be a solid mounting point for a T fitting. Personally I might be afraid to put any heavy fittings in the middle of a hard tubing run but I haven't done HT yet so I'm not sure what kind of weight it can carry unless it's on a vertical run. I'd look around on the web to see how hard tubers arrange their drain ports.