I do this with tomato seedlings...I have done it with pot as well.

As stated above a luke warm bath is best, but if rootbound, I have found that the peat inside the rootball won't wash out easily;
So I just transfer to hydroton filled netpot and no worries.

It is not as hard or scary as it sounds. Just do it. Make sure not to damage roots.

a third alternative I have found is to take a small container to act as an overflow tray and fill 1" deep with perlite. After that fill water to top of perlite, dig a hole for the plant and set in...In a couple of days the roots will have worked into the perlite, and thus you can transplant to hydroton filled netpots and no peat will fall into rez. Peace