Can workflow conditional rules be used to add related text for more than one checkbox item?

I have a question about custom fields. Is it at all possible to achieve this:

I have a checkbox list with around 20 items in it. When one or more checkbox items are selected I want it to display a text box where a user can enter a reference number.

Is this achievable with the workflows?

UPDATE:

If I create 20 text boxes and then create a conditional rule for each value in the checklist so that if item 1 is checked it opens a textbox for item 1 reference to be entered.

I did try creating one but when I tested it, the textbox field doesn't display. Here are my screenshots to show the settings. Have I missed something?

Kind regards

Mel