I can think of several off the top my head:

1. Use a programmed retrieve spec

2. Use a different form for the retrieval  which has a text box bound to that field instead of a radio button group. That way, you can just type =.

3. Add a text box to your form which is bound to the same field as the radio button group. Use programming to make the radio button group visible in Add and Update mode, while the text box is visible in Search mode. Again, then you just type = at the Retrieve Spec.

Will one of those do it for you?