As GRJ says, lighting up "specialty" cars like the PE observation car will take some manual manipulation and soldering. Here's one idea that may be so obvious that no one else has mentioned it. The LED strips are simply a collection of white LEDs. For the most part, you can simply replace an LED on the strip with another white LED on extension wires to reach special locations such as marker assemblies, drumhead fixtures, deck lights, whatever.
So here's an LED strip where I removed several of the surface mounted white LEDs and attached wires to the solder-pads going to various types of white LEDs. No fussing with resistors, wattages, capacitors, etc. etc. One of the "external" LEDs is from the strip itself with wires to extend it off the strip. This allows you to convert the LEDs intended for illumination into specific function LEDs such as marker, head/tail-light, dome, drumhead, etc..
I realize this is not a PE Observation car, but here's a caboose where a surface mount white LED on wires is powered from the LED strip and by GRJ's lighting board. The LED goes into an un-lit marker assembly with 2 red lenses. Let there be light!
Note that many styles of white LEDs can be purchased pre-wired on eBay or from model railroad suppliers. In other words, the difficult soldering (attaching wires to the tiny LEDs without destroying them) is done for you.