All GPS manufacturers use propreitary map formats

There is no map file standard in use anywhere

So yes, it would be possible un the following circumstances:
1. You know the BMW map file format
2. You know the Garmin map file format
3. You are sufficiently clever to write a file converter

But as the info is deeply secret and carefully guarded, you would find it near on impossible to get the file format info

and then you'd find it very dificult to write the file converter