We can only have one prompt type at a time. We cant combine both. The work around I was thinking might sound a bit odd
Create two parameters. one is dynamic (where you will have LOVs), one is static, with the same logic and make them both optional. So if user wants to select values from the list, he/she would select first parameter and leave the 2nd one blank. In the same way user can enter their own values in 2nd parameter and leave the first one blank.