The girl I dated before I met my wife was what I would call converted and the key was at first not to overdue and after building the relationship, explain what it is about tickling her that you like.
After going through a drought of ticklish girlfriends, I met "Kim" who had a striking resemblence to Rachel Welch. This girl was hot and most of all, extremeley ticklish.
She was a grade behind me in high school and we talked occasionally and one nite I saw her at a bar and she told me about how she just broke up with her boyfriend and one thing led to another and we ended up at my house.
Kim was very tipsy and asked me to take off her strappy high heels and in doing so I found she had very ticklish feet and spent the night tickling her all over,
Seeing how she never objected, I tickled her on other dates but she told me she hated it so I backed off. She thought I tickled her to be mean and I felt this was not the time to tell her that it turned me on.
Months into the relationship when we were snowed in at her parents house, I got the nerve to tell her I wanted to tie her up and tickle her feet because it turned me on and after going into detail about she told me I could.
You see, Kim was basically a nympho and loved sex and when she found that I liked tickling her to get sexually aroused and not to be mean, she was all for it.
After a little coaching she became a tickler's dream. Not only did she let me tickle her anytime I wanted she would actually promote it and would role play. She also never had a problem with being tied down and she also let me roll her up in a blanket so that I could tickle her feet. Anything went as long as it led up to sex.
At the bar when we would slow dance, she would whisper in my ear that she wanted me to take her home and tie her to the bed and tickle her feet until she passed out just to give me an erection on the dance floor.
She would also role play in different ways in that she would be submissive and beg to be tickled to death or she would be a defiant bitch who after tickling her would then beg not to be tickled. She also did a Russian spy interrogation thing where she would dress uo all in black and I would tickle her to get information, she would even try to talk in a Russian accent which she would loose after several minutes of being tickled.
The problem was with that is that I would get so turned on, the ticklings only lasted about fifteen minutes and I couldn't hold back having sex.
Anyway, my point is to be patient, work on the trust and explain that you can't really explain the tickling thing but that you love to do it and not because you want to be mean but because you love it and that she drives you wild.