Dont know if this would be possible but to create projectiles maybe a new tool or something to "glue" particles together? but still allow them to move? so for example "glue" stone particles together and use air pressure to move it, like a cannonball. Dont know if its possible but hopefully can be done.
well just using any particle is what i mean. like even metal, goo,etc. This "glue" element would stick the area you have highlighted or what ever and allow it to move but stuck together.
I reckon an options menu with "Gravity ON/OFF" would be great. Although walls would have to stay put but everything else would fall and move. Glue would be great to stick together powders and then they should be labelled "CMB" (combine) or something on mouse-over.