Dear Sugano ,
I can try to sort out your issue. U want to book an liability since your term are FOB shippin point. You can create an seperate account under payable - say for example Order L/C _________( and vendor name). This account you can credit when u get the information of Shipping and Debit Accrued Purchase - L/C. By doing this your liability will be booked. One actual receipt of the material you have to follow normal proceedure in AX. After confirmation of Quantity and invoicing you can reverse the first entry. This is a long cut but we are also following this since AX do not allow this functionality.
If you find this solution is ok then follow it or if you have find any other work around then please share with me.