There are several ways around any questionable ethical problem (though since holodeck characters are non-sapient, I can't really think of one that holds up) I can think of, including:
1. Program in a pre-existing "sexy story" and change the image parameters of the characters. (Easy)
2. Program in a set of personality parameters that means that the character fancies you. (Normal)
3. Program the original personality parameters and actually act out an entire courtship and relationship. Set right what once went wrong, or - if you're infatuated with a celebrity - create the ultimate self-insert fiction (Legendary)