I don't know if this is going to work on the 430, or any other panel mounted unit, but it's very easy to add own (additional) vector layers to Garmin portables:
- Use Google Earth Pro, ExpertGPS or any other GIS program in order to create a .shp file with the information you want to add.
- Convert the .shp file to an .img file using ExpertGPS (make sure that the projection is correct)
- Upload the .img file to your unit using ExpertGPS, MapUpload, or any other program.
- Voilą!

It works like a charm in several of Garmin's aviation portables. We're frequently uploading own vectors on our GPSMap 296, GPSMap 495, Aera 500 and GPSMap 695/696.