If you go big additions in the last 20 min, you may end up getting most of the way to the IBUs you're looking for, depending on the alpha of your hops and where you load it. Looks like you've got 5 oz in the recipe, you could play around in your software and see what you get if you put them in late addition. With 1 oz additions at 20, 15, 10, and 5, you'd be getting an end loaded version of the 'semi-continuous hopping' and that would probably put you in the 40+IBU range with your specs... perhaps a bit on the low side, but you could shift them around or bump some up with another ounce or so... If you are looking to do a single hop beer with something like Amarillo, I do think you want to focus on late additions, where it may take more hops to get the bitterness you want, but you'll be using those hops to get the aromas and flavors the variety is known for...
PFC, Arachnid Deployment Division
In the cellar: Galaxy Pale, Citra Pale, Honey Common
In the fermentor: Cat Yakk Saison
In the works: Wooden Cider