How to apply buffer in MapServer WMS query?

Question

I am trying to add a pixel buffer around a WMS query in MapServer. I noticed in MapServer/mapwms.cpp there is an option to set 'tiled=true' which should check for "tile_map_edge_buffer" "100" value in the map config file. However, when I check the spatial query, it doesn't seem to extend at all. Even altering SQL query to include extra data using ST_Expand(!BOX!, 0.01) doesn't help - the query does return extra data but it is not drawn.

I need this as I am generating point data through WMS EPSG:4326. The point data is displayed as large squares (changes with zoom level) but the data from the next tile near the border don't get generated in the tile of interest.

For example if the point on the main tile (lets say 100x100) is on (50,1), square size 20 pixels, the main tile generates a rectangle approx: (40,1 40,11 60,11 60,1) (20x10) which is correct. If I try to generate left side tile, I would expect to see the remainder of the square but I don't.

Anyway, if anyone had luck setting up pixel buffer for WMS, I would appreciate their input.