NSM doesn't currently offer supporting document ability. Submit an enhancement request explaining what type of information you would like to capture on the analysis. Specifically, what content is in the analysis report that can't be captured on the analysis itself.
You have a few options without an enhancement:
1. Depending on the volume of analysis reports you could evaluate putting the attachment on the associated specification (or nutrient profile). The linked specification on the analysis can be followed to see all attachments.
2. Create a DRL document named in a way that it can be manually associated with the specification. Multiple reports can be attached to the DRL document. You could also create a single DRL document per NSM analysis report. In either case, a manual DRL search would be performed to find the associated document.
If you feel users will interact with these reports often then you could also deploy a small technical customization(s) to improve the usability. For example, you could add a link to the NSM Analysis object. When selected it finds all DRL documents that contain the analysis or spec # in it's name.