Hi Sun.
KKF1 cant explode BOM. This tcode is intended for simplified production.
You have 2 options in order to do GI.
1: Create a reservation in MB21 with movement 261 with refference to the CO Order, Then you can do a GI in MIGO (or MB1A, MIGO_GI, or... ) . This is a good way to work bec you can separate responsabilities between shop floor ppl and inventory responsible. Also, you can print the reservation in order to do tipical inventory control activities.
2. The other option is just do the GI with reference to the CO order in MIGO, you only need to add a new pos and compleate the info (movement 261, plant, storage location, batch if needed)
Just an advice, if you are asking about explode BOM, i guess your customer is able to create this stuff in the system so, why dont implement a simple PP model that only do BOM explotion, GI and GR? A good PP boy can implement something like this in just few weeks. Your client can activate other stuff like MRP, Capacity Planning, batch determination and other stuff later.
Arturo.