You could use a prompt to display the contents of the field in an input box where it could be copied. Only drawback is that you are limited to 254 characters. I tries to use a dialogbox but that did not work and still honored the prevent copy setting. To use a prompt to display your field value for copying do this:
On your form create a field called Body1.
Place a button next to the field with this formula:
@Prompt([OkCancelEdit];"Copy Box"; "you can copy this text"; Body1)
The text in the Body1 field will be placed in the prompt's input box where you can copy it (limit of 254 characters)