The key is getting the glute completely relaxed. It may indeed bleed a little bit, but if it does so to such an extent, as you stain your carpet, there is definitely something wrong with the injection technique. It is alright to inject while in bed, but make sure that you don't activate your glute muscle when trying to reach it. Ideally, it is always best to get someone else for the glute injections. Also, doing more frequent rotations will give your glutes more time to recover.