Errr wasn't trying to incite anything man just thought about it and figured you could make it work. Making a last is a completely different skill set from making the boot or shoe. But if you have an understanding of where things need to be, by using a cast and adding to it for form and fit I would think someone who was not specificaly a last maker could make a decent one specific to the wearer. If nothing else this experiment on ones self would teach you alot about lasts... and it would be fun
Personally I love to reinvent the wheel. Making something by following a set of instructions or a formula only allows you to follow in someone elses foot steps. Gathering general information and doing it yourself probalbly wont yield nearly as good results.... but ... you can honestly say you made it, and if you enjoyed it you have learned and can improve it...and its fun
Hobbies should be fun.... if they are not .... find another hobby