You can specify that text in a bubble should be rotated by some amount. To do this, bring up the pop-up menu on a text bubble (right clicking does this in general) and select the "Rotate text" option. You should now have an indicator line that follows the mouse. As you move the mouse around, the text should rotate to follow.

When you have found the proper rotation, click to set the text rotation.

Constraining text rotation

Hold down the shift key to constrain text rotation to 45 degree increments.