Most of those LED remotes seem to use the NEC IR protocol @ 38kHz.
Your suggesion about using an opto-coupler is possible. However, you would really need to:
- have an oscilloscope or Logic Analyser
- You could hack the IRremote library an change the "mark" and "space" finctions to provide de-modulated outputs instead of modulated outputs, which would feed into the output of the IR receiver.
- be careful, IR receivers use inverted logic & you would have to allow for that in your design.
Alternatively, if the receiver for the light strip is concealed in a box, you could use the Arduino to receive all signals and then have an IR LED controlled by the arduino (inside the same box as the LED receiver), which just relays the signal you want to use for the LEDs. Seems like the simplest approach & also provides isolation.
In fact, you could just enclose the IR LED and the Receiver in a blob of blue-tac or play-doh! or just insulation tape as a physical shielding mechanism.