Pass row number to action in context

I have a webform which has a multi-valued entity reference field to include a list of users. When displayed in a view I see a row for each user, eg:
-------------------
SID 1 | UID 1
-------------------
SID 1 | UID 2
-------------------
SID 2 | UID 1
-------------------

I have a custom action triggered through the Views Bulk Operations module and I need the UID, however the context provided to the action only has the submission ID and not the view row number.
Is it possible to support this? From what I can see the context needs to come from here, not the Views Bulk Operations module, but I may be wrong.
thanks!