I did a 9 month old smack pack of oktober fest lager. stepped it up in several goes, it took 3 weeks in the end, but I got it up to a proper pitch rate for a high gravity lager. I did the first two steps at mid 20's, and then the last step at 13 degrees so I could taste it and get a feel for the flavour. Tasted fine, so I pitched.
Now, whether this was WORTH doing or not money wise.... I utilised some excess wort I had, so I didn't have to buy heaps of DME. But, DME ain't cheap, so there's always a trade off.
But it' scertainly possible