Presto multi cooker sous vide- clarification?
The standard hack is to use a PID controller.  IF you google, you will find many articles detailing exactly how, such as this detailed one from Over Engineered.

There are now also a couple of vendors of moderately low cost circulators intended specifically for this application such as Sansair that you insert into a pot or cooler.  They are new to the market, so there are some early adopter issues being reported, but the idea is quite elegant.