Same source OP-AMP summing/adder circuit?

Say you have multiple circuits running off one battery (+12v).

Say the output of circuit #1 oscillates about +1.5v amplitude of 1v. (+1v - +2v)

I can't modify circuit #1. But I want to press a button, and while that button
is pressed down, offset the output of circuit #1 by +1.5v. (+2.5v - +3.5v)

Can this be done using the one battery used for all circuits?

Thanks,
Rey

I'm sorry for my bad english but i'm Italian....

you can adjust the offset by plugging the voltage offset to the offset pin of an Operational Amplifier with gain=1

or you can build an Adder with an Operational Amplifier..

you can plug the inverting input with a resistor=1K to the ground, the out pin to this pin (feedback resistor) with a resistor = 1K and at the non inverting input you can plug your signal by a 330ohm resistor and the offset signal with an other 330ohm resistor (both resistor have a pin plugged to the same pin of the IC)

This is how I would do it: