I have figured a way to easily adjust the slots for any thickness media, it is really quite a simple idea so not sure why it did not dawn on me earlier. Unfortunately you cant do this in SCAL so it will need a bit of inkscapery - if anyone wants it adjusting for a particular media thickness and cannot grasp Inkscape give me a shout and I will do it for you and post it here

***EDIT***
Apparently you can do the slots in SCAL..
Import the file, ungroup
Select the slots object, in the properties panel set to Shadow and adjust shadow size to suit slot size you want
Select both objects and Path->Back minus Front
The file has two objects, the red filled spider parts and the blue stroke slots. If you wish to re-size the model (it is currently A3 which makes a spider about 220mm x 220mm x 85mm high) then select both objects and group them to resize together then ungroup again.
If you prefer inkscape..
To make the slots the correct size for your media, select the blue slots object and set the stroke width to slightly less than the thickness of your media - for 1mm board I used 0.8mm - then do Path->Stroke To Path.
Now select both objects and use Path->Difference.
That should cut the slots in the model suitable for your media and you are ready to cut

Here it is..