I have a g10 smart card (http://g10code.com/p-card.html)
This wouldn't be a problem at all. As you see in the picture in your link, there is a version with a smaller form factor (ID-000). This is the same card just with cut outs. Everything outside the contact area is just plastic. I made you a drawing in paint showing where the actual IC is in the card. Everything outside this box can be removed without any problem.
(copyright of the picture: g10 Code GmbH, I stole it from their webpage. My modification (red square) is released as CC-0)
If you have a strong flashlight (you should have one, they are awesome) you can use it to "see through" the card to check that. That can also be used to see the antenna on RFID cards for example (where drilling holes can be a problem)
This scenario is kind of inverse of how people want to disable PayPass/PayWave in their banking cards. There's a number of useful links in this question, search for "kill PayPass" for more. The most practical approach so far is drilling or punching a small hole through the antenna which runs alongside card perimeter. This of course requires locating the antenna so that the antenna is cut and no useful circuitry is damaged.
So it requires locating the card circuitry - same problem you faced. This is usually achieved with source of bright light, usually an LED flashlight - you put the card such that it blocks the flashlight beam and usually you can see where the antenna wires and chip are located - all the rest is just plastic and isn't requires for the circuitry operation.
Choose hole location such that it's not very close to card perimeter (otherwise the card can tear apart), not very close to any circuitry (otherwise mechanical stress can damage that circuitry or you can interfere with its functions) and doesn't compromise non-electronic features of the card such as possible photos, logos, embossed text, magnetic strips and the like. The linked to question links to a post where cardholder drilled the card right through magnetic strip - mileage may vary after that.