Several options:

1 Put in a ballast/load resistor in parallel with the LEDs (I have a spare set of resistors if interested, set up to plug into a trailer wiring connector).

2 Put in a solid state heavy duty flasher.

3. Modify the flasher module to take out the current sensing feature:
- http://www.pirate4x4.com/forum/showthread.php?t=511438&highlight=flasher