ATK's method, while it may reduce the canned taste, has two primary outcomes:
- It heats the pumpkin puree
- It reduces the water volume
The flavor intensification is due to the reduction. If you are not willing to change the water ratio of your base recipe, there is litte point to doing it, and then adding the water weight back.
So the question is: does bringing the pumpkin up to a simmer in a pan actually signficantly reduce the canned taste? While I suspect it doesn't at least when the final cooking stage is included, it is a pretty easy step to do, and won't cause you much trouble other than an extra pot to clean.
While you may need some trial and error, increasing the percentage of pumpkin solids in your swiss roll recipe will reduce the structure of the cake; it may tolerate a small increase (perhaps to the 1 full cup or even more, reduced slightly if you want to) without becoming too soft to roll.
While raw pumpkin is about 90% water I suspect the Libby's product is already reduced, to probably 70 or 80% water (I was not able to find a definitive answer), you may want to reduce your total pumpkin down by 2/3 to 3/4 of the volume above the base 3/4 cup called for in the recipe to keep the total liquid close. So if you add 1/2 cup of pumpkin, for a total of 1 1/4 cups, reduce it by 3/8 of a cup; this would be easiest done by weight where it is 3 ounces.
Pumpkin and eggs are the only signficant water in that recipe, so you cannot substiute out another liquid to allow you to bring in more pumpkin.
Finally, consider that product vendors are especially motivated to write recipes that show their products in good light, and are reliable. There is almost certainly some margin of error in that recipe for experimentation to account for the variance of their customers' cooking habits, but it quite likely close to ideal already or they would not have published it.
Best Answer
The most common, almost canonical brand of canned "Pumpkin Pie Filling" in the US is Libby brand. While the canned pumpkin puree is just canned pumpkin, the Libby "Canned Pumpkin Pie Filling" also has sugar syrup, natural flavoring, salt and spices. So I would add the spices, salt and condensed milk in @Phrancis's recommendation to 30 ounces of pumpkin puree (probably without the cornstarch, there is probably cornstarch or other thickener in the rest of the recipe, if not, consider adding it as a part of the next step I am recommending here), more or less of the spices and sweetener to taste. The eggs and dairy (other than the sweetened condensed milk, which would serve in the substitution as the sweetener) are most likely in your recipe, not expected to be in the can of "Pumpkin Pie Filling").
You want a texture pretty similar to the unadulterated canned pumpkin product. If your substitution is a bit thinner than the the canned pumpkin was (as it should be, with the addition of sweetened condensed milk) simmer it a while to reduce. That can get your volume down to 30 ounces and intensify the pumpkin flavor, making your substitution probably better than the stuff for which you are substituting. Libby sells the pumpkin puree in 15, 29 and 106 ounce cans.
BTW, America's Test Kitchen does that reducing trick to canned pumpkin just routinely to give it a more intense pumpkin flavor and to eliminate "the taste of the can".