If the thought of mentioning role playing to your partner in a face-to-face conversation is completely terrifying, then send your lover an email or text that details your erotic fantasy.
Have an open and honest conversation with your partner. If you are shy about discussing these details in person, you could establish the rules electronically via email or text.
It is best to keep it simple in the beginning. For example, you could wear a wig, or experiment with your make-up. Alternatively, you could grow or shave your facial hair, or wear an outfit that is not your traditional style. A small physical change can make you feel like someone different and will help you get lost in your character.
If you are confident in your acting ability, you could try a more elaborate role and talk with an accent.