Excise capturing without base value

Dear CIN Gurus,

There is a very specific scenario for which I need your help. We have Lump Sum Turnkey Contracts where the vendor gives a ceiling excise amount for which he will give the excise invoice. This ceiling excise amount has no base value on which it can be calculated. The excise invoices given by the vendor will be from the third party who is the material supplier for the contract completion. Please suggest me a way where I can capture the part 1 entries as well as posting of excise invoice.

Regards,

Ashish Dhawan

9990800147