We ran into the same issue... Ended up building our own TabBar so we could capture every state. Unfortunately all our widget code is tied up in a start-up, so I don't have permission to Open Source it, but it wasn't too hard to make.
It looks pretty much like the Widget 1.0 bar, just with borders....
Really, the biggest thing I think Corona is missing from "Business Apps" is the ability for things to Align to screen borders and to each other.
In the app above I have some helper functions that push objects into specific regions. It works something like this...
snap:above(customTabBar,snap.screenBottom) snap:above(twitterIcon,customTabBar) snap:left(facebookIcon, twitterIcon) snap:right(appleIcon,twitterIcon)
This sets customTabBar.y to display.contentHeight - customTabBar.height and makes it take the full display.contentWidth. The the twitterIcon gets placed just above, facebook to the left, etc.
So no matter what device you are on, those bottom buttons stay where they should be.