Sure, if you're doing a Pumpkin Porter who can pitch on top of the other cake. No problem. If you've got room that is. A lot of people who have too much trub from the first pumpkin to add another 5.5 gallons to the carboy. And it is going to ferment big so you'll likely lose more through blowoff.
Of course rinsing some of the trub away is easy enough if you do have too much stuff at the bottom when it comes time.
On Tap: 1. Kelly R. IPA, 2. Roter Hund Hefeweizen, 3. Bud Killer Blonde, 4. Red Dog Pale, 5. Roter Hund Oktoberfest, 6. Pumpkin Ale, 7. McRed's Stout (with new nitro system and stout tap,) Cream Soda, 8. ESB # 3, & 9. Ordinary Bitter.