I'm just seeing your question now. You may have found a solution, but this took me a while to figure out, so I'll respond anyway.
To get the passed values, go ahead and create your HTTP Endpoint and add a new operation triggered by it. Then, in your new operation create a script with something like the following:
$SalesForceID = $jitterbit.networking.http.query.Id $UpdatedStatus = $jitterbit.networking.http.query.Status
You can then use these variables elsewhere in your operation chain.
If you want to use these values to feed into another RESTful web service (i.e. an HTTP Source), you'll have to create a separate transformation operation with the HTTP Source. You'd set that source URL to be: http://mysfapp.com/call?Id=[SalesForceID]&Status=[UpdatedStatus]. I'm not sure why, but you can't have the script that extracts the parameters from the Endpoint and the HTTP Source that uses those in the same operation.
Cheers