The behavior you observe is due to the formatting rules associated with Times. Please start by reading my answer here: Returning an unevaluated expression with values substituted in. We can apply a similar technique here though the result is not quite as desired:
SetAttributes[hf, HoldAll]
MakeBoxes[hf[args__], fmt_] := Block[{Times}, MakeBoxes[HoldForm[args], fmt]]
hf[1/2 * 3/4] // TeXForm
$\left(1*\frac{1}{2}\right)*\left(3*\frac{1}{4}\right)$
This form is due to the internal format of 1/2 and 3/4:
Hold[1/2, 3/4] // FullForm
Hold[Times[1, Power[2, -1]], Times[3, Power[4, -1]]]
I believe this can be handled as you wish with a new MakeBoxes rule but it's Christmas and I've got other things to do. :-)