This is how I would do it:
 
1. Add the BKBMMSTR to your report again.  You will get a message indicating it is already in the report and will be promped to give it an alias name.  
 
2. Name it BKBMMSTR2.
 
3. Clear any automatic links that were created and create a link from BKBM_COMPONENT in the BKBMMSTR file to BKBM_PARENT in the BKBMMSTR2 File.
 
4. Repeat this procedure as many times as you need to depending on the depth of your BOM's.  We have 4 levels so we have 4 instances of the BKBMMSTR File. (BKBMMSTR thru BKBMMSTR3 all linked as described above.)
 
5. Create your report using proper grouping and sorting methods.  You can pull part descriptions by linking all Parent and Component fields back to BKICMSTR File BKIC-PROD_DESC Field.