Here's an idea:
case fan
Foam block x2
USB rechargeable battery pack
DPST toggle switch
1. Take your fan, clean all the extra crap off it.
2. Hit the plastic winder with a hammer. get rid of it.
3. cut the power cord about 6 to 7 inches away from the fan. Do not throw away excess wire.(step 2 was for fun)
4. Take block number 1 carve out a hole for your fan. About half of the fan's depth, right in the middle of the
block. Scalpel should work well for this.
5. Do the same with block number 2.
6. make a hole the same diameter as the fan in both. I would use a heated, long, skinny knife.
now comes the difficult part.
7. Take block number 2, bottom left corner of your fan well, or whichever corner the wire comes off the fan drill
a inch deep hole for the wire.
8. Cut a hole from the top for your battery pack.
9. Pull fan power wire through your wire hole, and up through your battery pack hole.
10. strip an solder to one end of your toggle switch.
11. take the plug end from leftover wire and cut about 2 inches back from the plug.
12. strip and solder to plug, being sure to match correct wire with correct side.
13. plug to battery pack.
14. stuff battery pack in it's hole.
15. top with switch.
16. glue block 1 to block 2, with fan in the middle. Let dry.
17. Carve block 1 to fit into your intake, as well as block 2 to not be so huge.
Voila.
You now have a removable intake fan that is battery powered. Stick it in your backpack, put it in your tank bag, make it into a necklace!
Pull it out when things get HOT!
That was mostly for my entertainment. Someone please make this.