Look up one of these give cars to friends glitches that are working, and have a friend give you a BMX bike. If you have to store it in your MOC just take a car from your facility afterward and swap it
Unfortunately it's Tuesday so any give cars to friends glitches that may have been working probably will not be working much longer
Or use a SV/aircraft to personal vehicle storage glitch. Take the bike in place of aircraft. Also use a motorcycle you don't have copies of as the already stored vehicle, these glitches tend to swap PVs to your bike rack and you can't get them off, but MC spawm menu seems to see motorcycles in ALL types of vehicle storage areas.