Ok, I played with it some more and it appears it won't do what I want.
 I'll have to hunt some more, or code my own solution.

require 'rubygems'
require 'highline'

h = HighLine.new
a = []
a << "a a a a"
a << "b b b b b"
a << "--Some more text-- --Some more text-- --Some more text-- --Some
more text-- --Some more text--"

puts h.list(a, :columns_across)  # explodes [1]
puts h.list(a, :columns_down)    # explodes [1]
puts h.list(a, :rows)  # works, but not what I want.
puts h.list(a, :inline, " ")  # wacky


I'm looking to create the equivalent of this:

a_a_a_a__b_b_b_b__--Some more text--
__________________--Some more text--
__________________--Some more text--
__________________--Some more text--
__________________--Some more text--



[1]
/usr/lib/ruby/gems/1.8/gems/highline-1.2.0/lib/highline.rb:362:in
`ceil': Infinity (FloatDomainError)
        from /usr/lib/ruby/gems/1.8/gems/highline-1.2.0/lib/highline.rb:362:in
`list'
        from ./test.rb:19