usage of FRC1 condition to split cost equally for PO item

Hi Gurus,

currently for FRC1, i can enter the freight amount for per kg at the PO header and it will then calculate the freight cost based on the item total qty(kg)

which means if i enter $10 / KG for FRC1 in header conditons.

for po item 1 with 5 kg, it will auto calculate FRC1 as $50

for po item 2 with 6 kg, it will calculate FRC1 as $60

for po item 3 with 10 kg, it will calculate FRC1 as $$100

now for my new requirement which users does not want to trouble themselves to calculate the FRC1 into by per KG, is it possible to just key in the total freight amount for FRC1 like $210 and let the system auto calculate the FRC1 for each PO item based on each item total quantity(kg)??

if so, how to set it up in the conditions type?

the nearest i can find is FRB1 but it's calculate based on PO item material price...i want it to calculate on PO item KG..

thank you very much.