How about I use to have weakness (blah) However doing xyz I have overcome it.
I understand your point and you need to be really careful with that.
So for example I use to be anxious with difficult customers. discussed dealing strategies with management and other colleagues, had some training now I see dealing with troublesome folk as one of my strengths
You need to remember that the second you say anything that could be considered negative the interviewer will stop listening. I have been on the other side of the table and when I hear anything negative I take notes and underline in big bold strokes. It can certainly throw an interviewer off so its a knife edge to balance.
Interviews are more about the techniques you use to convey a point rather than the content. You have to come across as a person who they want to employ. The interviewer has seen numerous candidates and has heard all the usual responses. Trying to use a textbook response can be detrimental.
Be yourself and be honest. Let the interviewer keep control and let them guide your answers. Be confident and try to sound genuine rather than having a canned answer.
My personal weakness is my kids. That is nothing to do with the job and is specifically personal to me. In an interview I would give that as a personal weakness (used as a positive) and let the interviewer decide and lead where that applies to the job. I then hit them with the coping mechanisms and how I would make small sacrifices because in the long term it benefits my kids and the flip to a positive is in my control. Not once does that become a negative toward the role advertised.
EG.
ME: My weakness is my children.
DM : Working shifts means you lose some important days
ME: I maintain the balance. I may lose harvest festival but I get Easter and vice versa.
DM : What if you lose both ?
ME : I make other days more special. Its just a change of perception. I accept a shift worker life because the benefit is that I get other days that some parent don't
DM : So you are sacrificing your children for a job ?
ME : I want the children to be proud of me and being a Train Driver allows me to do that. Its an important job and doing the best I can in that role makes them proud.
Seriously you can flip a weakness without saying anything negative. Again; that is me and it is personal to me. There is no black and white response and any interview should flow naturally. Even online applications aren't black and white. The generic response is said by everybody.
Strengths and weakness' are a personal thing.