Braintree credit card holder (custom fields)

Hello,

I want to have some custom fields in my Braintree subscription in my Spark application. For example - I need credit card holder name and address to be passed to Braintree. I've added custom fields in Braintree panel but it doesn't show them in Braintree form (during payment). The only fields I have during payment are: Card Number, Expiration Date, CVV, Postal Code. How can I add anything else? Also. I see in database that Spark has added columns starting with billing_*. Why are they empty? Is that because I use Braintree? I saw that when using Stripe payments there are more filds to fill up during Subscription process. Is there any possibility to integrate them with Braintree?

Halp. Thanks.