Asp.net - Getting Information (on Click) That Was Used To Programmatically Generate Asp Controls?

How may one get information that was used to programatically generate asp controls?For example, I pulled a DataTable of user objects from the database and have organized them on a page, listing groupings such as a list of employees directly under the employer for each employer. On the page, I list each user's Username as a LinkButton. When I click one of these employees, I want to redirect the page (which is easy) and set a session variable to the selected user's UserId (which seems not so easy). How can I pull this UserId value back? These elements are not hard-coded with nice names (as they are generated in a for each loop).

Code from comment below:

Dim lnkbtnPm As New LinkButton ' is my link button. '
lnkbtnPm.Text = pmDr.Item("Username") ' where pmDr is my datarow. '
lnkbtnPm.CommandArgument = pmDr.Item("UserId")

[code]....