Information needed to mark user as attended

First of all, thank you for this great module, it is a tremendous help - although I have run into a bit of a quandary I'm hoping you might be able to assist with. I am attempting to build a VBO list of all users who have signed up for a node to replace the VBO administration list that functioned in D6 but does not in D7. I was hoping to mimic that functionality by having a VBO trigger various rules for the necessary actions such as bulk marking users as attended or not, canceling user's signups etc. I am able to get this to work halfway, but am not sure what I need to pass to the "mark signup attended" action to make it take the currently checked user and mark them as attended on the current node. I have tried loading signup data and making lists containing the user and the node, but I always get a second page asking which user and/or node I wish to use in executing the rule. What is the proper way to accomplish this?

Thanks so much!

David