Another option:
Code:
on *:text:*hello*:#: {
  if (%flood) { return }
  set -u4 %flood On
  msg $chan $chr(160) hi $nick
}

160 is a non-breaking space, and it doesn't get stripped away, so effectively there's one special space and one normal space, which results in double space.

You don't necessarily have to use the $chr identifier, you could just put those non-breaking spaces there manually: //clipboard $chr(160) and paste away!