[Node]

I would not worry about wiring. This way you will power the car through reverse protective diode within FET controlling that indicator. It could probably handle couple of continuous amps or so safely (at least), so if you do this as quick as possible (just power on, unlock, disconnect within couple of seconds) in normal circumstances it will actually work.
Now the main question is why battery went flat. If it was just left for too long, ok. If there is some fault in the car which actually consumes high current or if you try to switch on ignition while powering that way, you may be needing a new LCM or replacing that FET.
There can also be welcome lights coded on, which will be activated right after unlock, thats why I propose to remove power ASAP after unlocking. That diode should handle them for a couple of seconds, but not for very long.
If you have power supply with current limiting capability, use it for safety, but note that central locking will require some amps.

[Taj786]

Thanx everyone, will try on thursday as i got day off work, battery died because it was just left, no faults.

[Node]

I just thought that maybe you could use starter clamp for powering the car from underside if you can raise it. Would not need fiddling out with indicator. Not sure if its accessible from underneath but if it can be reached, may be fastest and simplest way.

[JIMMYQ]

JIMMYQ, thanx, wont this indicator trick cook the wiring loom?

no it wont you have to be quick as mentioned in the previous post by node but it will definitely work and do the trick and give it enough power to work the remote