The link referenced above has disappeared from it's original website, and is only online in PDF format here:
Link
Basically it involves doing some surgery to the heater box under the front bonnet. No need to pull the dash etc. At first what is being proposed here may seem too good to be true. let me assure you, it works. After about 3 hours of following the instructions, I now have all the heat I could possibly want, and I've stopped the foam blowing out.
When you read the instructions, at one point the instructions mention using electrical tape to cover the door with, it will make sense when you read the process. I have an improvement to offer. I used a silicone adhesive to glue a plastic cap on the hole you have to create to do the surgery. Worked great, and I think will hold up to the heat better.
i did this months ago, and it has worked perfectly since then. Still get a random piece of foam blowing out, but most of it came out in the first week after the repair.