I really don't think you need to go to all that trouble. My FSJ heater running on high will melt ice on my windshield. The stock heater is basically the same parts. If you aren't getting much air to the defrostor, I would suggest cleaning the cowl air intake, cleaning the heater core box out and making sure the flaps are in the correct position to get the air to the defrosters.

We haven't had real ice this year. But, during one of the bad weeks a year ago, it was very thick. I drove the M715 to work one of those days. It stayed in the parking lot all day. They called off Colton's school at 1400. I left work early to go pick him up and my door was frozen shut on the M715. I wrestled the door open and got it fired up. 10 minutes later, the temp gauge moved off the stop. 5 minutes later, I turned on the defroster fan. I was driving away a few minutes later with a clean windshield. No ice scrapper was used.

If you are determinded to "fix" it. There are some things on e-bay every now and then that mount on the bottom of the windshield frame that extend the defrost channel across the entire bottom of the frame. You might want to look into that. PM Snuffy for a picture since he has a set of them.