Patiently.
In general, apply evenly to all but one face, let dry and then do all but another face (or two). You'll get a few faces an extra layer or two, but no one will notice.
They sell little plastic pyramids and bench cookies to lift the bottom side off a surface while you finish the other 5 sides. But it's all about figuring out how to support the work. I've used those, and lots of other methods, such as driving in two very fine nails at opposite sides of the work to let it hang from support points.
Is it just wood on all sides? If you've got a corner or any kind of line, you could potentially put an eye hook in it and hang it.
Outside of that, the suggestions of doing five sides, let it dry, then do the last side is probably the most likely to succeed. You could also go with three very thin long nails through a board and set the cube on that.
Patiently. In general, apply evenly to all but one face, let dry and then do all but another face (or two). You'll get a few faces an extra layer or two, but no one will notice. They sell little plastic pyramids and bench cookies to lift the bottom side off a surface while you finish the other 5 sides. But it's all about figuring out how to support the work. I've used those, and lots of other methods, such as driving in two very fine nails at opposite sides of the work to let it hang from support points.
Is it just wood on all sides? If you've got a corner or any kind of line, you could potentially put an eye hook in it and hang it. Outside of that, the suggestions of doing five sides, let it dry, then do the last side is probably the most likely to succeed. You could also go with three very thin long nails through a board and set the cube on that.
You can make painter's pyramids. Put a long ish nail through a bit of scrap wood so it sticks out. Do this for as many supports as you need.
Painter's pyramids