you pretty much have to recirculate or constantly stir to avoid stratification / overheating the bottom of the mash. and even if you constantly stirred with a spoon, you arent going to be moving much of the liquid below the FB.
It seems that this is not a popular option but it seems to me it would be less likely to burn or scortch or carmelize than rims
why do you think that? to me, it sounds like its more
likely to scorch than RIMS. with RIMS, you have nice, fast and even flow rate over the entire surface of the heater, which you will not have in a setup like you describe, even if you constantly recirculate it.
there are good reasons why this method is not popular (and not just unpopular- but ive never seen it attempted even once, although the idea has been brought up before). not to discourage innovation or anything, but i think your time and money would be better spent some other way.