Execution factor must be an integer multiple of the header factor

Hello PS Experts,

We are using CN08 to create Projects from a Sales Ordes, I just have a question if for example I have the following position:

Material               Amount

XYZ                      10

On my Project I have a Network XYZ with Execution Factor of 10 and since the Execution Factor in the Template is set to 1 for the Activity of that Newtork my Activity also has an Execution Factor of 10.

The customer  wants to "split" the Execution Factor either adding a new Activity on the original Network and then Setting the Execution Factor to 5 in the new Activity and 5 in te original or by adding a completly new network with no link to the Sales Doc. (these one can have the Exec. Factor of 5 since is not linked) but the Execution Factor of original Activity cannot be less than the original 10 or else the following error occurs

"Execution factor must be an integer multiple of the header"

Is it possible to do this? what could be the correct approach?

Thanks ind advance.

Regards Ed.