Personally, I run separate wires to a separate power supply since I use a ton of fans

For me, because I want them all controlled individually via the internet.
OVERKILL!

Personally, I run separate wires to a separate power supply since I use a ton of fans

http://www.thingiverse.com/thing:527337

However, since the v6 is shorter, this would create an airflow misalignment as jagowilson can attest. It requires said carriages, but would cool layers which have already been extruded and cooled, meaning small perimeters and top layers would suffer in resolution.

BUT! you have a few options:
1) Rework Lawsy's fan mount and upgrade to his carriages. Jagowilson has just done the latter on his SD4 with great success if you need guidance
2) Remove the provided enclosure entirely and set up a desk fan set to blow directly at the printer (I have done this with success)
3) Switch to other materials like ABS if possible. We all understand different models require different requirements, though.
4) Wait until jagowilson gets done with his fan mount design.

With PLA, heat is an enemy. It takes too long to cool. So until you can actively cool extrusions, I recommend door #2 and wait a short while.

For the stock carriage there should be something you can design a part to fit around, clamp on, something... Always a way the linear bearings mod just has accessory mounts on the carriage already so it's easier.

I see you have an SD4. That means your x carriage uses linear bearings. Before I swapped to the lawsy carriage I was going to design a part to clip where the bearings hang. You could always try that. Perhaps use the screw holding the bearings on as a bolt.