How to combine grid and list settings in Bourbon/Neat/Bitters?

Question

I am trying to restore the default list behavior (li's display property is 'list-item'), but in the same time make the list in two columns (li's display property is 'block'). Is there a workaround?

<!-- HTML -->
<ul>
  <li>Letter 1</li>
  <li>Letter 2</li>

// Sass
ul
  @extend %default-ul
  li
    +span-columns(6)
    +omega(2n)

Sass below works, but I wonder if there is a more conventional way.

ul
  list-style: disc outside
  padding-left: 5%
  li
    display: list-item !important
    +span-columns(6)
    +omega(2n)