The only way I know to do it is this.
1) Create the conference rooms as Permanent rooms (bottom checkbox when creating) (as a side note, once rooms are set up as permanent, they can be bookmarked on the Spark Client as well
2) Log into the spark client
3) Click on the conferences tab.
4) Click on the room you want to auto-start. Check the option that says "Join on Startup".
When you do this, the Spark Client will automatically join the conference room when the end user logs on, and the conference window will pop up.
