Question: Is there a way to do a substitution in 2-D Math format?

I'm doing some algebra with transfer functions, which are often written in LaPlace Transform notation, e.g. f(s) = 1/s.  One often wants to find the "gain and phase" of such, which is easy to do using the following steps:

1) Substitute "i omega" (imaginary unit, omega = frequency in radians) for s.

2) Express the complex quantity in polar (rho, phi) notation -- rho = amplitude, phi = argument (Phase).

So here's my question -- if I am developing a document with the math entered in 2-D form, how do I do a "subsitution" of "i omega" for "s" in an expression such as 1/s?  Is there a 2-D equivalent of "subs" command?

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