custom apm variable for AD password expiry

Customer wants to disable the option of giving " change AD password before expiry" on F5 APM login page, but want to show custom message to the users before 7 or less than 7 days of password expiry. So I have disabled the option in AD query. But it's not setting the APM variable pwddaysleft.

How to derive and set custom APM variable for pwddaysleft using AD attribute pwdlastset in F5 APM? is there any TCL script that can be used?