I would remove the "would you be willing.." it makes it sound like you are allowing him to control you
I would just say "I need to switch.." and see if he objects... Don't give him the idea he can call the shots... he's been doing that for a long time... an assertive note that isnt' castrating is certainly acceptable...
You aren't asking him, you aren't telling him to shove his priviledges etiher.. you are jus INFORMING him and exiting...
I would also add a note to explicitly ask him NOT to be present on your birthday and to NOT contact you for ANY reason...
"I would like to have my birthday independently from you this year... I want a day free of her and unfortunately that means a day free of you"
I know this sounds harsh, but it does send the message across..