While the opening of the pocket is tough to alter, you can remove the pocket lining and make it to fit what you are going to use.
If ohio got a clue this will be something I start messing with since I like the idea of having this option and I consider most of my pockets to not be deep enough to hide the butt of a small glock or a small revolver.
The pants others have mentioned have fairly deep pockets from the get go, I prefer to mess with what I have rather than getting rid of decent clothes that fit.
I also recomend getting a pocket holster or making one, I have seen them for not too much money and a pocket holster does several things.
It keeps things away from the trigger of the gun. It also keeps things from getting into the barrel of the gun or between the slide and gun frame. A hanky is going to add more pocket lint to the gun and this is not something that is really great for reliable firearm useage. Some holster have an open area where the barrel of the gun is when fully holstered, others are closed.
Since pockets are not the cleanest area I prefer a closed setup that is as strong as others mentioned when doing a trigger test.
And I fully understand you consider this option as the last thing before leaving the gun home, but with practice the pocket carry can be just as fast as iwb carry when done properly.
My opinion, I am certainly not an expert.