1st gen. contact sensors won't mount on my doors because of rounded mouldings

I bought a 1sst gen. alarm system a few years ago and I'm finally getting around to installing it. I just discovered that these contact sensors won't mount on my doors because my door casings are rounded, so whichever piece I put on it points inward. If I put a wedge to straighten it out, it's too high. I see there's an extension, but it's only available for the 2nd gen. and I'm definitely not buying another one. I figured I'd post this issue here. I can't be the only person who has ever experienced this.