Check insertion of Travel Expenses inserted from user portal

Dear SAP Gurus,

is it possible to insert a R3 control that check the number of Travel Expenses of a certain type (f.e. "meal") that the user inserts from SAP portal linked to a single trip, f.e. an user exit I can use?

I don't need this control when you try to save the trip, but when you check the Travel Expenses insertion.

Thank you, best regards.

Stefano