Hi,
This functionality was added in 4.2.0 to make it easy for people to use custom product types.. funny, I was very surprised that you'd have posted about this problem, didn't occur to me that you'd not be on the latest version (4.4.1 :) ).
Upgrading will take just a few minutes, then all you need to do is add to that file and support for your custom product type is instantaneous. :)
Saying all that, I've just realised that, outside of the Revision History, I haven't documented this functionality anywhere except in that file itself. Guess I should a wee section to the configuration docs - more work to do then!
Have a good day! New update of Ceon Manual Card to get sorted here..
All the best...
Conor
ceon