Your problem is NOT that you need an quick-and-dirty training program. As an ex-IP you will be entitled to an FAA CFI cert with instrument and airplane single or multi ratings (maybe both single and multi, depending on what airframes you taught). Definitely do the paperwork drill and get your CFI certs.
Sheble, ATP, etc. are designed for people who already have general aviation skills and knowledge and just need to punch their CFI ticket. You are the opposite...your ticket is already waiting for you, all you have to do is file the paperwork but you need to make sure you get the general aviation skills and knowledge before you go try and teach.
Since you were an IP long ago, and you probably don't know much about FAR part 61, I would suggest that you find a local school or CFI who can walk you through as much of the ground and flight training as you need to prepare you for the type of instruction you wish to do. This will not be legally required, so you can be very flexible, but you really do need to get trained on piston maneuvers and part 91 and 61 rules...especially part 61 as it pertains to flight instruction. You can do this at your own pace.
I don't see a need to attend a full-time formal training program, unless you have the time and money.