How can we add additional logic to Web ADI

Hi,

We are using Web ADI and GL Integrator to upload journals to GL. Is there a way to put in additional validation logic before the journal is uploaded? Logic such as "IF the Journal Category = Fuel THEN Journal entry lines DFF Attribute1 should be populated". If the Attribute1 is not populated, the validation should fail and give the user an error message "Please enter the required Attribute1". Is there a way to incorporate such logic - something similar to custom.pll for forms or OAF extensibility for the OAF pages or some other way? 

Any suggestions are greatly appreciated.