1) Go near a big lake out of roboport range
2) Equip landfill
3) Create landfill ghosts with shift-click in the lake; create whatever shape your blueprint should be
4) Capture the landfill in the lake with a blueprint as usual
Result: You have now a landfill blueprint, which makes filling large lakes easier.
Edit: As of 0.13.9, this doesn't work anymore
