Go into your preset's folder, and open preset_#.material (it won't actually be a numbersign, rather the actual number of whatever preset folder you're using) with notepad.
The easiest way to do this is to open notepad, go to File, Open... select "All Files" from the dropdown, then navigate to the file.
You'll see a bunch of lines of material code.
Scroll down til you see this section: (again, the # sign will be the actual number of the preset folder you are in.)
material preset_#_maneMat
{
technique
{
pass
{
lighting off
cull_hardware none
cull_software none
scene_blend alpha_blend
depth_write off
texture_unit
{
texture preset_#mane.png
}
}
}
}
highlight that section and replace it with this:
material preset_#_maneMat
{
technique
{
pass
{
cull_hardware none
cull_software none
alpha_rejection greater_equal 128
texture_unit
{
texture preset_#mane.png
}
}
}
}
You will need to manually replace the # signs with the number that matches the preset folder and rest of the code.