How to insert a pre-defined number into user db

[ChurchMedia]

Using the useradmin_edit_column2 and the userdata_start plugins, I need to insert 3 values into the user table. The trick is that 2 of them are input values and one of them is the same value as one of the input values. So like this:

$value_1 goes into field_1
$value_2 goes into field_2
$value_3 = $value_2
$value_3 goes into field_3

I know how to use input rows for the useradmin_edit_column2 hook, but I don't know what to use or how to format value 3 (which needs to be the same as value 2 and silently go into field 3). I've tried using standard PHP code, but it's not working. I think there's a vb class that I just don't know.

Any help would be appreciated. Thanks!