I'm afraid there isn't a way to use it from VB Script. The new UIA COM API introduced in Windows 7 is usable from C++ clients and .NET clients (through COM interop), but the older IDispatch technology that VB script needs isn't implemented. We focused on the highest traffic interfaces: native C++ and .NET.
The only solution I can picture would be to build an IDispatch-compatible COM DLL, perhaps using ATL, that would take calls from your VB script and then call through to UIA. You wouldn't have to replicate the whole UIA API -- only as much as you were using. But this is still hard work.