Grouping fixtures for effects engine

So, I have a 3x5 grid of RGB LED fixtures I built using LED tape. Is there any way to group the fixtures together so that effects fan across them in groups. Say I have them addressed as follows:

1 4 7 10 13
2 5 8 11 14
3 6 9 12 15

If I wanted to do a chase across them and have them light up in columns (1,2,3 then 4,5,6 etc.) how would I do this?
If I select them all and just do fan I get the cascading effect of them lighting up individually, which is neat, but I would like more control.