Sales order for Assembly to plan the Child Part of BOM - No Production Order.

Customer is asking the following scenario:

We are producing the following items, FG1 & FG2. Customer needs 1 x FG1 and 1 x FG2 to complete one assembly.
Material Type - FERT - Finished Goods

FG1 - customer part number HKMC1
FG2 - customer part number HKMC2

Set of 1xFG1 + 1xFG2 - customer part number HKMC3

Customer required to order either FG1 (HKMC1) & FG2 (HKMC2) separately or to order Set of FG's by using HKMC3 number

Eg: PO-NO. 123456
Item1: HKMC1 - 500 pcs
Item2: HKMC2 - 500 pcs
This will be normal Sales Scenario - No Issue

Or

Eg: PO-NO. 78901
Item1: HKMC3 - 500 pcs
Is there an possibility to tell the system what to plan if customer is ordering by using the HKMC3 part number ??

We don't want to create new production order to create a set of FG1 and FG2. It needs to be combined in a "Sales" BOM.

HKMC3 is just the packing of one HKMC1 and one HKMC2.