Thanks un33 but that looked way too difficult for this little black duck. So I had another think and in the end it wasn't that hard. Laborious, but not hard, and all within the functionality of SA.
I had about 15 of these multitaskers so I created an access rule for each of them, then just added their user level number to the group access rule for each page they have access to. Messy, but it works.