How does Tim Allen follow up his $140 million The Santa Clause? Any way he wants. Walt Disney Pictures has commissioned a sequel from screenwriters Steve Rudnick and Leo Benvenuti and, according to insiders, the company is willing to meet Allen's $7 million asking price, though a second Clause won't see theaters until 1996. ''Tim wants to take some time off,'' says Allen's manager Richard Baker. ''There probably will be a sequel, but he will almost certainly not do a Santa movie for his follow-up.'' But the real reason lies in the effort it took to transform Allen into jolly old St. Nick. Says a Disney exec: ''Tim (isn't anxious to) put on makeup for five hours every day.''