I've been to Solitude and talked to both Legate Rikke and General Tullius. But both haven't got any option to sign up.
I've tried using "setstage CW01A 1" but this doesn't add the quest at all.
Starting the second quest with "setstage CW02A 10" does work and starts The Jagged Crown but it gets sort of bugged as in the Stormcloaks don't see me as an enemy and will never attack me.

I'd really like to be able to join the Legion and start with the default quest, but I'll settle for a way to fix the bugs and go straight to the second quest.

What about that other dude in the room? He should point you to Rikke...

He does tell me to talk to Rikke but Rikke doesn't have any options beside some history and info.
Strangest still is that the setstage command doesn't even work.