I wouldn't try it   I would be very tedious.  Either use it as is or buy what you want.  That is a decent price,  I sell the 1" Inswool for $9.00 per foot.  It would be much cheaper to buy just what you need, unless you were planning to re-sell it or go into the business of selling forges.  For a forge built with a 20# Propane bottle you would only need 2 feet, then what would you do with the rest of the roll.  Some of the makers over on other forums do recommend using 2" blanket.  Personally I think it is overkill.
Let me know if I can help you.