Auto-fill specified characters of passwords

Almost every bank I’ve used has had this security measure, and whilst I agree that it is annoying and bad practice from the bank, I doubt it is going away any time soon and would love some sort of function that can allow the autofill of a specified character position. I tried custom fields but unfortunately it doesn’t work as the custom field IDs are numbered as 1, 2 and 3 rather than the actual character positions that they are requesting (which changes each time).