I would like to create some math channels using parameters I am reading in from a .dsd file. For example, I am reading in parameters x(t), y(t) and z(t) from a previous data acquisition and would like to create a math parameter w(t) = x(t) / 60. Is there a way to do that

If I understand it correctly, you would like to add a live trace of previously measured data. This is possible if you export these channels in the text format, then add a reference curve in the math section and paste the data.

It is the best to go to reference curve setup, press copy, paste it in Excel or Wordpad to get this:
t [s] Value
1 1
2 3

and then replace the values with real values from your text file and the Copy-Paste it back to reference curve.

You can define also a trigger when the reference curve display starts (if that is not start of measurement).