automator File renamer Variables Sequential

Hi
I’m trying to create a script to help me with some batch file renaming
In this example I would like to change the following file names:

MVI_0001.MOV
MVI_0002.MOV
MVI_0005.MOV
MVI_0006.MOV
MVI_0007.MOV

to

$A_$Slate_tk_01.MOV
$A_$Slate_tk_02.MOV
$A_$Slate_tk_03.MOV
$A_$Slate_tk_04.MOV
$A_$Slate_tk_05.MOV

I wish to add a couple of variables such as
$A for which camera it was, could be A,B or C
and
$slate for the slate number

so far I’ve i’ve built the workflow as follows
Get Selected Finder Items
Ask For Text (Camera)
Set Value or Variable (Camera)
Ask For Text (Slate)
Set Value or Variable (Slate)

this all works fine,
I found this handy page showing use of this automator action called Rename Finder item by Pattern
http://usefullittlethings.com/renaming-files-on-the-mac-with-wildcards.html

I can follow the use of ‘Rename Finder item by Pattern’ but I dont know how to add the variables into the new file names…

thanks for any insight…