I tink there's already a mod. If there isn't:
Try setting up a square image in MSPaint with one pixel being equivalent to one Blocko (or 2x2, 4x4, 8x8x, etc). Make a circle that fills up the entire image. Copy the circle over into Blockland. You might need to mess with the canvas size a bit until you get the right dimensions for what you need.
Only did it once, for
this. Worked great. Most of the time I just mess around in-game.