Three options:
1) Buy the new adapter that shims the H3-3D down away from the shell, and includes longer legs to keep camera off the floor. Not sure if this part is shipping yet. If not, probably very soon.
2) Dremel a sufficient hole in your shell, similar to the hole in the new P2. Search this forum for many instructions/photos/videos on this.
3) Try my cheap quick hack that avoids Dremel and new part, if you have the longer screws that come with the prop guards: use those plus 4 rubber faucet washers to shim the H3-3D base plate away from the shell. I still have enough ground clearance (barely) though I always hand launch and hand land, so ground clearance not a high priority for me.
Kelly