I'm officially confused.
I had thought you were saying:
Data from SQL is brought into the form via a secondary data connection and displayed in my form
I want users to select rows from this secondary data connection and do something with them
It sounds like what you mean is:
There is a repeating node in my main data source for my form
I want users to select rows from this main data source and do something with them
If the data you want users to be able to select is in your main data source, simply add another field with a data type of boolean in the same group as the rest of the data. Add the field to your repeating table as a checkbox. Your qRules command can then be filtered to use only the selected rows.
Is the query field in your web service connection repeating?
And, I'm sorry, but are you really wanting to select rows in a repeating table, or to use a multi select list box? I'm confused by that, too. :)