Hi Michael,
The custom properties in 4.5 aren't listed directly, however you can map
them. When you are in the dialog where you would pick what property to
map to, there is a "custom" button. Simply type the exact name and data
"type" from the Inventor property to create it. This will then list it
and you will be able to map it.
In 5 we show these automatically.
Cheers,
--
Thanks,
Brian Roepke
Product Manager, MSD
Data Management