How can I poke a hole in the roof in Dwarf Fortress?

I'm making my underground farm in a new fortress, and I thought I would try a new way of getting water to it, going UNDER a lake.

I assumed I would just have to mine under it and the water would fall through. But of course I forgot the floor of the level above.

My question is simple: How can I poke a hole in my roof?

For a another view of the issue, here are some pics.

Level 1

Level 0

Build an upward ramp on the square you want open the ceiling on, then go up a level and order that square channeled out. They should be able to reach it at that point.

If that doesn't work, building an upward stair and then telling them to dig the downward stair on the square above will.

Of course, either way whoever does the actual digging is going to get hurt when a lake's worth of water hits him right in the face...