A few people have tossed around the idea of the Twins calling up Francisco Liriano and sticking him into the rotation without pulling anyone out. Ninety-nine percent of the time, a six-man rotation simply serves to deplete the talent and take pitchers out of their rhythm, but I think this might actually work for the Twins.
Certainly, a six-man staff would mean fewer starts for Scott Baker, the Twins' true ace, but it isn't as though the team would be adding another fourth or fifth starter. Adding Liriano could well have a greater impact than the Cubs adding Rich Harden or the Brewers' acquisition of CC Sabathia.
It also means one-sixth fewer starts by Livan Hernandez; hypothetically, the Twins could pitch Hernandez strictly at the Metrodome, where he is 8-1 with a 3.91 ERA (which compares favorably with his 2-5, 7.48 mark on the road). Less Livan is the best thing the Twins could do, especially if Liriano is the beneficiary.
The reason this makes sense for the Twins this season is the almost equal play of the Twins' other young starters. Stats aside, on any given night the Twins could get a stellar outing from Nick Blackburn, Glen Perkins, or Kevin Slowey.
They could also see any one of those guys get rocked in the early innings and end up with a long night for the bullpen. Additionally, if the Twins make the playoffs, they will need all of these guys to be in shape, and an extra body in the rotation could allow for fewer innings during the stretch run and greater strength in the playoffs.
The down side of starting this plan now is that it would knock these creatures of habit off their normal routines, which would probably prevent the Twins from ever taking this route. Going from a five-day regimen to a six-day would take at least some adjustment time, and that isn't a luxury the Twins have.
The Twins are in a dogfight in the AL central, and will be for the near future; they cannot upset the fragile balance of the rotation, even for long-term benefit. Once they realize that benefit, it may be a moot point if the Sox and Tigers get hot.
Realistically, the Twins wouldn't keep a six-man rotation all season, but, rather, would probably go with it until someone started to falter down the stretch. At that time, the stumbler would head to the bullpen and the rotation would shrink back to a traditional five-man circuit.
The six-headed monster is almost never a good idea, but the Twins could be one of the few teams that could actually pull it off. However, since they didn't start the season that way (and rightly so), I highly doubt they'd risk messing up their young arms for the sake of trying something that may or may not work.