PIC12f683 Ext IRQ on non-IRQ pin

Wanting to use MCLR as interrupt port change state - its set high. Prefer to use weak internal pull-up.
Tried this:
ioc.3=1; intcon.GPIE=1; //enable IOC bit for GP3, then GPIE
//in ISR checked for state when button pressed high to low thusly:
if (GPIE && intcon.GPIF)
//nosuch IRQ not being called
The logical port to use would be GP2/ext int port, unfortunately thats taken for something else.
If not possible on GP3 perhaps GP4/GP5 but have to turn off oscillator gates to stop internal oscillator and set the port high with weak pullup. Have had no joy there either. If anyone can point me to more information appreciated tks.
Alistair.

Hi Alistair,

There is no weak pull-up for GP3 when it's configured as I/O. You'll need to add an external pull-up.

Regards, Mike

Deleted; wrong forum. Sri