This doesn't sound exactly like what that extension does, but it might be something good to look at to get some ideas. (Hopefully it's open source!)
Thanks!
One of its features is that you can pop comments sections in a <pre>...</pre> block to stop Comment Reflower doing anything to them. Here's an example, where you can see that the preformatted section extends past the wrap column.
// Watford DDFS reads by initiating a multi-sector read,
// counting sectors read, then doing this when it's got
// the data it wants:
//
// <pre>
// 0D43: ldy #$60 A=00 X=FF Y=60 S=DC P=nvdIzC (D=60)
// 0D45: dey A=00 X=FF Y=5F S=DC P=nvdIzC (D=D0)
// 0D46: bne $0D45 A=00 X=FF Y=5F S=DC P=nvdIzC (D=01)
// 0D48: lda #$D0 A=D0 X=FF Y=00 S=DC P=NvdIzC (D=D0)
// 0D4A: sta $FE84 A=D0 X=FF Y=00 S=DC P=NvdIzC (D=D0)
// </pre>
//
// The loop at D43 is $5f*(2+3)+(2+2)=$1df=479 cycles, or
// 240 usec.
(In the long run, ideally, I suppose, you'd want your code text editor to support a wide range of formatting options, so that you could have italics and bold and monospaced and all sorts. But if you just decided that initially a simple proportional/monospaced font switch would be useful, this is the sort of markup you could use to key the transition off.)
Even if this doesn't do exactly what I'm looking for, it will definitely help give me some ideas on how to do what I want. It is indeed open source, and it looks like VS2017 support was added a few months ago: