paypal订单摘要的自定义属性/多重税?

I am not sure whether i am asking an obvious question here. but i couldn't find any suitable variable for following case in HTML Variables for Paypal Payments Standard documentation.

1) How to configure extra attribute with own defined label to be shown on order summary page. Let say i would like to have:
number of person: 2
Extra description: abcsd.

2) How to configure multiple tax of different label? The default i found is label with tax and only 1 tax?
GST: 10%
Service Tax: 6%

Both of above seems to be a simple implementation to me, but i just couldn't find the solution using the documentation.

1) You can use the "custom" parameter to include any custom data you need to pass in the request. The field is literally called custom, and you can send up to 256 characters in this field.

2) Payments Standard only supports passing a single tax amount (that you calculate yourself) or a tax rate that would be calculated against the order amount. If you need to separate different tax rates/rules, you'll have to do that in your own shopping cart / order system.