Get Keychain to remember an additional field I regularly log on to a financial website using Google Chrome

This requires me to enter a Account number, a password and also an Employer number.
I store the Account and password in my Keychain, but have to enter the 8 digit Employer number each time.

Is there any way of getting Keychain to remember this additional number.
There's no way to force Keychain to store the additional field.

I use 1Password for things that Safari/Keychain refuse to remember.
You can manually add fields for sites such as banks [at your own risk] where credentials will not auto-save.

There's also LastPass, but I haven't tried that