Well, it is only a basics trick that came to my mind this night....
This trick is based on a electronic switch IC for both analog and digital signals.
The IC is the 4066 (you can also use the older pin compatible 4016 which has higher "ON" resistance)
The concept is simple:
We connect the ISP or UART signals (any Ardruino user here) to the A channel of the IC.
Then we connect the B channel to any device we want ( especially that naughty pin consuming LCDs!!!)
All the C channels of the IC are connected together and then to the reset signal.
As the reset line is high (via the 10k resistor) the switch is closed so the A and B channels are connected
thus we have "talk" with any device connect to the B channels
When reset line is HOLD at ground the switch is open and we can not talk with the external device.
NOTE that the switch is open (no connection) as far as the C channel is HOLD to ground.
Ardruino uses a boot loader.... This means that every time reset is issued it runs first the boot loader...
The reset line is NOT hold to ground when programming so you gotta MODIFY the bootloader
to hold an extra pin to ground when programming and then disconnect the pin.
This pin is also supposed to be connect to +5V through a 10K to 4K7 resistor.
So this circuit is NOT recommended for inexperienced ardruino users...
At the other head, those who program with ISP will find this circuit very useful cause it saves some extra pins
for other uses.
Simply all the C channels of 4066 are connected to the reset pin and MOSI, MISO, CLK to the A channels separately.
At the B channel they can connect anything that comes in handy in the respective pins (An A channel is interconnected to a perspective B channel)
NOTE that if you weren't using any resistor on the reset pin as pull up resistor, now it's required.
Although modern ISP programmers doesn't seem to have problems with devices connected to the ISP pins
it's been times I had much of a problem.... So the circuit is recommended...
Hope, I've been of help and not a headache...
Best Regards, Lefteris