Easier detector placement?

When the size of a detector changes then the position of that detector and all downstream detectors must be manually updated in each of the macro files so that the distances between detectors does not change. This can be quite tedious and time consuming. We have quite a few macros for various baseline FPF setups, I'm wondering if it would make sense if we instead specified the detector order and the separation between each detector in the geometry macro instead?

i.e. add commands like:
```
/det/detectorOrder FLArE FASERnu2 FASER FORMOSA
/det/detectorSeparation 4300 1200 1200 1200 mm
```

I'm not sure exactly how to implement this, but I feel like such a thing should be possible within GEANT4