One way to do that in After Effects was mentioned by Brian Maffitt in an old Total Training tape and demoed at MGLA in 2003. Brian showed the creation a 3D volume of a human from scanned slices of some poor guy and said one might do the same with renders some Fractal Noise or similar as offset 3D layers. There's probably a variety of additional techniques found through some searching, though Photoshop text as 3D volume in AE might prove unwieldy. Andrew Kramer's cloud still as particles or smoke examples and Peder Norrby's Volumetric Smoke with Trapcode Particular might be leveraged too. One option no longer available is AE filter Aurora Sky, since it wasn't updated to 64-bit for CS5.
Here's Dan's psuedo-stacking example: