Custom Attribute

Greetings, Gurus!

I need to add custom attribute to SAP standard task, based on local portal UWL, without any connection to back end system.

When I try using the wizard to add the attribute for "uwl.task.coll.inprogress" by creating new configuration - I need to select the system in step 2, but the list of systems is empty, as my UWL is not connected to any back end system.

The question is - how can I use the local AdHocSystem, used by standard connectors, to add attribute?

Is this possible at all - to add custom attribute to standard task & task creation wizard?

Thanks in advance!