Paying network fee via UIA or BTS

[ebit]

 +5%

[xeroc]

The features is there already .. but only available to the blockchain level. It's not yet exposed to the end-user in the GUI

Devs are working on it:
https://github.com/cryptonomex/graphene-ui/issues/356

[gn1]

https://bitshares.org/technology/user-issued-assets/#fee-pools

Here, there is a paragraph that goes, "When a user wishes to pay a network fee with the asset, the fee pool will step in to convert the asset into BTS at the rate that the issuer has specified. This means that issuers may charge a premium every time users opt to use their asset to pay network fees rather than paying them directly with BTS."

This sounds like user has the ability to choose whether to pay the network fee using BTS or UIA. However, I don't see any section that allows me to choose to pay using BTS or UIA. System automatically tries to pay using UIA.

Where can the user switch this to whatever denomination he/she wants?