Sales Order fulfillment based on Base Unit

Hi ,

We  are getting problem while doing SO fulfillment based on Base Unit.

1) We have created units of measure as follows: (Name : GEN_UOM)

Name     Conversion Rate (/base)     Base Unit

EACH        1                                  yes

CSE          6                                 

PLT          12

2) We have created an inventory item (S9000)and given the following settings
Units Type      :  GEN_UOM
Stock Units     : EACH
Purchse Units  : EACH
Sale Units       : EACH

3) We have created a sales order  with Item : S9000 , quantity = 3 and units = CSE.

4) While doing  fulfillment we  want to do  partial fulfillment
( 3 CSE = 3 * 6 = 18 EACH)  . ie We  want give
quantity =4  , units =EACH in Item Fulfillment screen .(In this Item fullfillment screen  units