You can't really do that and it makes no sense to use a crosstab that way. If you are just trying to list the media values available in each territory, you could create a formula in the main report like this, basically hard coding the values:
select {table.territory}
case "Territory1" : "Media A, B, and C"
case "Territory2" : "Media A, C, and D"
//etc.
Then add this as your second row field and suppress the subtotal in the customize style tab.
Otherwise you would have to use a manual crosstab where you collect the media values using a variable and then display everything in the territory group footer.
-LB