LED rear signal bulbs

[ChrisZang]

So a while ago I switched my tail lights to smoked LED taillights, which looks damn good, IMHO
However the signal lights are still good old Thomas Alva Edison style bulbs.
I'd like to switch them to LED bulbs as well (I don't think that this would work with the front though due to the way they sit in the housing).

So back to the rear bulbs:
I understand that LED draw less power so you need a resistor so that the flasher relays will send current.

So I went to my local car parts store and looked for LED bulbs with a built in resistor, bought them and put them in, but still no go.

So here's the question:
Does anyone have made this conversion and got it to work?
(Brand of LED bulbs, or any other tips&tricks pls)

Thanks