Make sure you have no pour areas selected, and click the pour button. If they are on different nets the net dialogue box will say "different"
Click OK and hey presto all pours will be done one after the other. I use this ALL the time and its a great feature. Also if you click unpour button with NO pour area selected it will unpour ALL.
If pouring in same layer with embedded areas remember you may have to set a pour order value for each pour area (in the properties).
I didn't know that using Pour without any selected areas was possible, but this answers my question (altough I am aware that mis-pours sometime do happen, but my copper areas don't overlap, so in this case it should be ok).