Boiling just helps get out organic compounds and soluble materials such as pollutants that might be in the stone, and kills any parasites etc (only relevant if the rock comes from a freshwater pond or such). I don't think I've ever boiled a rock in the 15+ years I've kept aquaria and the rocks I've collected have spent years in succesful tanks. But then, almost all rock around here is a very safe (and very pretty) kind of granite.
If it's still possible without ruining your decor, you could just take the rocks out, dry them with a towel (no need to get them dry dry, just not dripping wet) and pour a little bit of vinegar on them. If you see it foaming or bubbling, the stone may slowly dissolve in your tank and raise your pH (and release potentially harmful compounds inside the rock I guess); if this happens, it's better to leave the rock out unless you have a specific reason to raise your pH. If the vinegar doesn't result in a reaction, just put the rocks back in. That's my opinion anyway.