It's worked for me by treating this as a given (given that I will be working for them, I will be at least maintaining the PTO that I had at my previous company) and by offering alternatives for HR. Sometimes companies have personal time that is separate from PTO. You often won't get this time paid out to you if you quit and still have hours but since I plan on using it all every year that's not a big problem. Some companies can give you extra floating holidays or other types of time off to make up the difference.

You usually only have to resort to that if the HR system is inflexible and someone is making a big deal about it. A blanket statement that we don't do that, can't do that and won't think about doing that is usually a bad sign.