Multiple choice different values & text possible?

Hi

I am looking for a way of using the multiple choice drop down & for it to display one thing as text then attribute a different value

E.g.

if i have a drop down to select country, I want the user to see the text “United Kingdom” but I want the value assigned against that choice to be “uk” – how is this possible?

I am using the add parameters to url bit after and need the value to be different to what the user sees/selects

Please advise?