You can easily accomplish this with the Transition -> Card Wipe. Create your lower third, bkg & text and precomp it. Now apply Card Wipe to your lower third. First set the "Back Layer" to "None" You will have decide how many "Rows" you need depending on the look you are trying to achieve. Set the "Columns" to 1. Change the Flip order to Bottom to "Bottom to Top". Now just keyframe the transition completion from 100% to 0%.
Here's an example project.
4501_lowerthirdwipe.aep.zip
Johnny Cuevas, Editor
Thinkck.com
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.