You can only change the location in the registry ...

• Close Outlook
• Create a folder where you want to put the IMAP datafile
• Copy the PST file with the name of your IMAP profile from C:\Users[Username]\AppData\Local\Microsoft\Outlook to the desired location (eg the new created folder)
• Afterwards, Click Start / Run and type "Regedit" (You'll need administrator rights for this)
• Go to HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook
• Add a REG_EXPAND_SZ (Expandable String Value) with the name: ForcePSTPath
• Fill in your new folder
• Delete the mail account
• Create the mail account again.  
• Start Outlook
• Your PST file will be created in the new location