Do it right or don't do it at all.
Take off your butt pad, which you don't mention whether it's a factory hard plate or cushion type recoil pad.
Use the base of this pad as a template to mark out wood, plastic or even metal, such as aluminum, so you can cut out/drill holes with enough thickness to get the LOP you require. I usually make these up with 3-5mm thick plates.
You don't mention the type of stock, other than it's wood.
If you're planning on adding length to a collectible rifle, such as a full stock milsurp or Winchester lever action, the rubber butt pad would be your best choice, if it has a curved butt plate.
The late model 94 rifles, other than some of the Commemorative types, had flat ends on the butts to attach the butt plates.
Making up "shim" type plates is easy and they can be finished to look very nice. They can also be utilized without devaluing or altering your existing stock.
Don't glue them, just slip them together and get some proper length screws to torque the plates down. Unless you use very slippery material, they won't move.
I personally don't like the look of spacers made out of the sidewalls of tires, flip flops, or plastic buckets.
I have seen some very nice spacers made from 3/4 or 15mm belt scraper material, which comes in Red, White and Black.