You can see my solution at http://www.dave.burt.id.au/ruby/lcd_digits.rb

I used two functions, one to turn something like '9' into a big ASCII-art 
digital-looking 9, and one like UNIX's paste command to stick them next to 
each other.

Then like this:

 number = ARGV[0].scan(/\d/)
 puts paste(number.map {|digit| lcd_digit(digit, size) })

Cheers,
Dave