My doc was fine with it. I agree the CGM is a big help! I was in a similar boat, had 12-13 year old going "why don't you run a full marathon" after I'd run 2x 1/2s in 2 weeks in 2009. I ran Chicago last October and here's a shot of my CGM line including the race
I was pleased that BG was not a problem although horrible cramps were. I wrote a lot of stuff about the ups and downs and stuff getting pulled out of my abdomen in the "Diabetics Who Run Marathons" thread if you want to read back. It's probably sort of like a "blog" but there's other people kibbitzing and I liked participating in that group while I was training. I'm wanting to do it again this year to run more smoothly.