The only real reason for holding water back in a mashing that I have found is for the sparging of the grains. If you are not going to sparge then it really does not matter. The other reason for holding hot liquor back is for the reason of raising the temps for your different steps in the conversion stages. 100 deg. F. would be pretty low for a total single step and would produce a very dry beer. Heating the mash via an induction burner is great and all but you run into two issues.
1- Heating the mash can lead to scorching the wort or grains in the bottom of the kettle,
2- And stirring the grain bed of course eliminates the one purpose of letting it settle, Filtering the wort during your vourloff process and re-circulation!
If I were you, I would simply hold back some liquor in another pot, bring your strike water, approximately 1-1.25 qrts. per pound of grain to strike temp. Decide how many rests you want to do, I would suggest the first being the ...
(10 minutes) Phytase (86-126 F) – Lowers the pH of the mash.* Lowering the mash pH has a number of benefits, though a Phytase rest is rarely used by modern brewers.
then bring mash to..
(15 minutes) Beta Amylase (131-150F) – Produces maltose, the main sugar fermented in beer.
and finally the
(60 minutes) Alpha Amylase (154-162F) – Produces a variety of sugars, including maltose and also some unfermentable sugars.* Mashing at the higher end of this range produces more unfermentables and therefore more body in the finished beer.
After that is done, then you can sparge with clean liquor at 1680170 deg. to lock the sugar chains and stop the conversions.
Mashing at a lower temperature of 148-152F activated more beta amalyse, resulting in more maltose conversion.* Maltose is the primary sugar preferred by yeast, so a lower mash temperature results in a larger percentage of sugars being fermented resulting in a clean beer finish with higher attenuation, slightly higher alcohol content and less body overall.* It does generally take a bit longer for beta amalyse to do its work, so a longer conversion step at low temperature is needed.
Mashing at the high end of the range (154-158F) activates alpha amalyse, resulting in not only maltose but other unfermentable sugars.* Less of the sugars will ferment, leaving lower yeast attenuation and additional body in the finished beer.* Alpha amalyse completes its work more quickly than beta, so a slightly shorter step time can be used.
Hope this helps.
Cheers and good luck.