The iPad doesn't have the same richness of controls to adjust labels, unfortunately. I think the best you can do is to use the Geometry popover to turn the label to match the line, but as soon as you move the line to a different angle, you've got to repeat the process.
Good news is that it does heed the adjustments you can do with the Mac app. So, assuming you have the Mac application, make a stencil with a collection of lines with labels, set the labels to be parallel to the lines, and send the stencil to your iPad. Then use the Contact Omni button to let them know that having those controls on the iPad is important to you!