Cost center pick up during MIRO for Vat, service tax on purchase

Hi Expert,

Our client is project based organisation ans using both WBS element and cost center to capture cost in CCA.

client is having multiple plant (each plant is considered as seperate profit center) and wants to capture cost plant wise

when we are booking invoice through MIRO, VAT, SERVICE TAX (gl assigned in ob40) is getting calculated on purchase value but is askiing for CO object.

we tried to set defaul cost center in OKB9 against valuation area but it is not working.

is there any alternate work around to get permanent solution for this issue.

Regards

Sachin Indulkar