Custom Forms and Employee Center

I created a custom expense report to capture mileage.  My goal is to provide Employee Center users the ability to choose whether they use a standard expense form or the mileage version.

I am able to make either expense form show up in Employee Center as the *preferred* form, but employee users don't see the Custom Form field and therefore can't choose their form.

I have verified that the Custom Form field is included in both forms and is marked as mandatory... but it still doesn't appear for Employee Center users.

Is this a hard limit for Employee Center users?  Or is there some other step involved in making this work?