The problem with the low intensity circuit wired to the blinker and the high intensity path wired to the brakes is that the light will flash as it should until the brake comes on, then the light will be at full intensity and the flashing of the blinker won't be visible. That's what I meant by being swamped out. With the light at one diode drop (~.7V) below V+, adding another line to the light at one diode drop plus a resistor will not affect the light at all.

I would like to add that it is a great tip, just the listed application was faulty.