You would probably have to go with a shoulder rig. I don't think I have ever seen a IWB for a full size. I do have two leather holsters that I have tried to use with a longer shirt but it didn't work too well for me. I will have to dig them out and see what they are.
You could use a Fanny pack our other bag, but to me that is to obvious.
You could consider open carry if it is legal in your state. That would give you more holster options.
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