You can try BetterTouchTool. There might be a setting to do that. Maybe you'll even find another gesture to triple-click that you'll like better.

BetterTouchTool does not support two finger tap/click actions. There was an experimental version a long time ago but it was implemented in a 'hacky' way and never really worked right.

BetterTouchTool does let you set up a TipTap to middle click, so that you can press with a second finger whilst your first is down (sort of like a two finger click but with a delay) to activate a middle click:

→

Alternatively, you can set up a tap/press with three fingers to middle click in BetterTouchTool. This is supported fine:

If you're really looking for a two-finger click, KeyRemap4MacBook lets you remap right click to middle click using a private.xml such as this:

<?xml version="1.0"?>
<root>
  <item>
    <name>Right Click to Middle Click</name>
    <identifier>remapRightClickToMiddleClick</identifier>
    <autogen>
      —PointingButtonToPointingButton—
      PointingButton::RIGHT, PointingButton::MIDDLE
    </autogen>
  </item>
</root>

See private.xml documentation for more information and to limit to certain apps.