Deactivating 2 of the 3 lights would do a lot 
This was just a test and admittedly I was a bit too lazy to do the rendering again.
Changing to Canvas (I guess it's cardboard, so PP cloth might be closer than SEBS anyways) will likely help too. If you want to try yourself:
Might require an edit to the background.dat as well.

This was just a test and admittedly I was a bit too lazy to do the rendering again.
Changing to Canvas (I guess it's cardboard, so PP cloth might be closer than SEBS anyways) will likely help too. If you want to try yourself:
Code:
1 16 0 -24 0 1 0 0 0 1 0 0 0 1 YOURFILE
1 510 0 0 0 1000 0 0 0 1 0 0 0 1000 rect.dat
1 16 200 100 800 10 0 0 0 10 0 0 0 1 background.datMight require an edit to the background.dat as well.