There is one way, increase this season's payroll, which will automatically increase future season's payroll based upon your new payroll.
Your options are to transfer money from coaching or prospect budgets into this year's payroll (next year's will be 80% of whatever your payroll is this season, so every mil you add to this season's payroll will give you an extra 800k to start extending guys for next year before the season rolls.
You next option is by picking up cash in a trade. You can "sell" a prospect, for a piece of junk plus $5 mil from another team which would give you an extra $4 mil in next season's budget projection plan. Some worlds explicity disallow those kinds of deals, some have a group of owners that will veto a deal like that in a heart beat no matter what the league rules say, and some worlds won't even blink an eye.
You're other option, a variation on Option 2, that may get passed in a world that would normally veto a straight cash deal, is to send a prospect to another team, for a guy making $5mil + on the last year of his deal. The other team covers $5 mil or the remaining amount of his contract, whichever is less, will in turn increase your current season payroll and thus your future season budgets and perhaps allow you to extend that pitcher today before the season rolls.