MIMA will get you closer. If you get MIMA, you don't need a separate FAS switch. Or at least when I installed my MIMA a few years go it was integrated into the system. Also, MIMA is amazingly versatile and I don't think you'd need a brake/clutch switch mod. With MIMA you have COMPLETE cntrol of the IMA. As much or as little assist/regen as you want, whenever you want. You can also create automatic set-points for the assist/regen that fit your driving style/needs.
Adding an Enginer PHEV kit is pretty easy. Depending on your drive this would certainly bring you towards your goal. A 2kwh kit adds 85 lbs, though. That's what is in my Insight. I also use this as a way to grid charge the main pack.
You could also consider adding a grid-charger for the IMA battery. Insightcentral.net has some long threads about that.
As far as the stock pack. Even if you have to replace it for a reasonable price. Check
Hybrid-Battery-Repair for details. This is what it says on their site
"We repair Insight batteries for $750 - $1250 depending on how many internal components need to be replaced. The average repair costs only $1000."
I haven't heard of anyone making a SGCC. I think if you get MIMA, you'll have plenty to play around with.
What is your typical commute like? (distance, terrrain, etc.)