I guess it depends on how well you recover.  I think you'd totally be fine with a 20-25 miler at an easier pace 2 1/2 weeks out.

For my first 100, three weeks out I ran 26 miles at elevation on the trails, followed by 12 miles on a paved bike path the next day, followed by an easier trail 50K the next (total mileage for the week was 85).  The next week I just ran 27 miles, with only an 11-mile long run.  The next week I ran 24 miles with a 10-mile long run.

Although I believe I planned on having higher mileage for my second 100, I recall I got sick and it didn't happen.  Three weeks out my mileage was 65, including a 21-miler on trails, followed by an easy trail 50K.  The next week I was sick, so I only got in a 17-miler on the trails on the weekend and a couple of short easy runs during the week (total of 25 miles).  The next week I ran 26 miles, including a long run of 12.

For my upcoming 100 (August 24) I just ran a 50-miler this past weekend and will be doing three runs on the course this coming weekend (7-10 on Friday, 20 on Saturday, 31 on Sunday).  My plan has me running 40 miles next week, but I'm not sure what my long run will be (may be 20, or I might do a couple of shorter runs).  The following week I'll run about 20 miles, with a long run of 10.

I haven't ran a 100 yet although I am training for one in the fall.  At a minimum I would follow a marathon taper type of schedule the last two weeks.  If I hadn't agreed to be a pacer for a local marathon months ago, I would be running 20 as a long run two weeks out and  have my mileage about 20% less than normal, (for me 20% less would be about 70 MPW.)  There is nothing to be gained by running B2B long runs totaling 30+ miles two weeks out from your race.  As EDRW said, it is all about recovery...