Writing client-side operation participant for work item save

I am trying to write a client-side operation participant to participate
in WorkItemSaveOperation. In particular, I want to run some particular
code when the work item state changes from New to "In Progress".

I see from existing examples of server-side operation participants that
the OperationParticipant#getOperationData() method returns an instance
of ISaveParameter for the work item save operation. This is an API type,
so it's reasonable for me to grovel over this object and get the bits of
data I need. When I try to write the same participant on the
client-side, the operation data is of type SaveParameterDTOImpl. This is
not an API type, and doesn't seem to implement any API type. Thus, it
seems impossible for me as a client to get the information I need in
order to write my operation participant.

Is there any way for a well-behaved client-side work item save operation
participant to obtain information about the work item being saved?

Thanks,
John