Well, there don't seem to be any straightforward tools to do this type of reducing of transfer functions.
However, one thing you can do is to use symbolic variables, namely use "syms s" to define "s" and then type the transfer function out in terms of s. At this point, you can use the "simplify" command to, well, simplify the expression, and then use the "pretty" command to make it look pretty.
Another option, if you're trying to construct the closed-loop transfer function, is to use the "feedback" command when doing so. This function automatically reduces the transfer function to its lowest denominator form.