Change default operator of custom field from "Is" to "Contains"

I have created a custom field in my CRM transaction.  The field is set to an Uppercase Text field.  I have no problems entertaining the data and saving it.  When I try to add it to my list of search options it is only showing with the default operator of "Is."  When I click the dropdown list for default operators I do not see anything other than "Is" listed.  How can I change this to "contains" so that it can be searched more easily?

Regards,

Jon