You need for this an esf editor.
0.) Backup your startpos.esf which you can find in data\campaigns\main
1.) Start with Sweden a new campaign.
2.) Declare war to the factions.
3.) Save game.
4.) Open startpos.esf from data\campaigns\main with esf editor
5.) Open also the savegame in the esf editor
6.) Delete the whole folder campaign_world (subfolder from campaign_env) in startpos.esf and save
7.) Copy now from the savegame this folder back to your startpos.esf and save
And here is the tool:
http://www.twcenter.net/forums/showthread.php?t=260597