Hi,
0MATERIAL should already have an ALPHA conversion. If so, you do not need to bother about this. BW will automatically strip out the leading zeroes during reporting.
If you're using some other IOBJ for Material, make sure ALPHA is enabled on it.
But please do not change the Material length in BW (even if you use a custom IOBJ), your solution will be extremely fragile if you do that. Think about what would happen if the functional guys create Materials in R/3 longer than 8 characters. It could happen, and you would end up truncating the extra characters. Not at all recommended.
Regards,
Suhas