A problem with purchase of material and its usage in BOM

Hi;

I am using Vantage 8.03.408B
We purchase material from a supplier and let us name it as PART A and the unit of measure is NOS.
The supplier supply this material as PART A only and the unit of measure is same as above.
1 Number of PART A is a set of
Part 1 - 2 NOS
Part 2 - 3 Nos
Part 3 - 3 Nos
Part 4 - 6 Nos
Part 5 - 6 Nos
The design guys generally use PART A completely in the BOM but some times they need to mention only PART 1 - 1 Nos only in the BOM. Part 1 / Part 2 … etc cannot be purchased individually
Could any body suggest me how to handle this sort of problem.