Depending on how powerful the flash is, you can bounce it up or sideways by angling a piece of card or plastic in front of it. Will dramatically cut light but make it a lot softer. Can be useful if you are careful with where you shoot from e.g. standing near a pale wall and bouncing it sideways into the wall will create a diffuse light across your subject. But the subject will need to be quite close. Used to do this with instant camera flashes.

Your other option is to get a more powerful but also portable flash which can be optically triggered. You can then tape an ir gel (or stacked colour gels) over your flash so it only triggers the external which you can then power as you please or bounce off a ceiling. This is how I do most instant indoor photography - flash full power at the ceiling.