I don't know of a satisfying way to do that. Here is an approximation:
DisplayForm[
RowBox[{Style["]", 30], "\[NegativeMediumSpace]", 1/2, ",", Pi/2,
"\[NegativeMediumSpace]", Style["[", 30]}]]
The options DelimiterMatching and SpanMaxSize may have to do with solving the problem, but I have found no way to trick Mathematica into treating "[" as a closing delimiter, or "]" as an opening delimiter. TeX has the \mathclose and \mathopen, of \left \right commands that do that.
