Reducing Canned Pumpkin (as per America's Test Kitchen)
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.