I still have my preference letter that was given to me as part of my Bid Day present (since we obviously can't take it with us after pref), and this is exactly what it says:
Dear Jennie,
I am so happy to see you back here again tonight.
I know what it is like to be so far from home. Sometimes it can be a lonely or frustrating experience. After getting to know the women of Alpha Delta Pi, I found that it was possible to establish a family away from home. My sisters have been there for me through the tears and the laughter. I hope you find these blessings,
whatever your decision may be.
Sincerely, (Sister's name who preffed me)
We were always told when writing the preference letters to write about a special memory we had with the sisterhood, and then say something like the bolded part of my post (without guaranteeing them a bid). I know that the preference letter was something that helped me be certain that I really wanted to be an ADPi....it really helps if the person who is preffing the PNM has talked to them more than once over the course of recruitment (and I know that it isn't always possible for that to be the case, but if possible, I think that's the best way to go about it).
Best of luck with your upcoming recruitment!
And I'm not sure I understand....the writing of the preference letter is against NPC Recruitment guidelines, or is it specific wording that may sound like bid promising (even if that's not the case) is against the guidelines?