External Datasource 'Like' information

Is it possible to assign ‘Like’ information to fields in an External Datasource table, to tell Epicor that an External field should behave the same as an Epicor key field?

I am working on a Quick Search, currently using a standard BAQ but I want to change to an External BAQ. If I use a standard BAQ, the Criteria can be ‘smart’ and show search buttons or drop-down lists for key fields (JobNum or ProjectID, for example). When using an External BAQ, this doesn’t work, because Epicor doesn’t know that my External Datasource ‘JobNum’ field is LIKE erp.JobHead.JobNum.

I was hoping I could set this in External Datasource Metadata maintenance, but I only see options for setting field Description and Label text.