Which is why a lot of us feel that it's poor technique to try and be so precise with ferments.
It's hard to stop an active ferment, the only way you can read of some success is to cold crash the ferment for a week or so, but you still wouldn't really be that accurate as it would take a day or three to chill the yeast into hibernation, then once it's all cold/chilled/crashed, you rack it off any lees that has settled out onto stabilising chems - not a 100% guaranteed to work but it seems about the best way of accomplishing this.
Equally, it's usually easiest (take that as meaning more controllable), to start lower, ferment dry, then back sweeten. I'd guess you would need some residual sweetness to achieve that "maple syrup" flavour, because just the sap would have a weird, unfamiliar flavour.
So back sweetened to what ? maybe 1.020 or a little more ? If you back sweetened a bit too much, I'd have thought that some acid addition would mask just enough of the sweetness to still retain enough of that wonderful maple syrup sort of taste.
good luck with your batch McJ, maple syrup is too expensive here, to try for anything other than a 1 gallon batch. Even then it would likely have to be used for back sweetening a traditional to retain some of the flavour/sweetness - I'd guess it's cheaper over your side of the pond......