There are several ways to taper a pill.
If it is not delayed release or extended release and not expensive..
> You could dissolve the pill in a measuring flask of water (e.g: 100ml) and drink a fraction of it (e.g: 90ml, 80ml).
> You can use a nail file and shave off a certain number of strikes from an end.

For something like Cymbalta with pellets inside, I had to line those pellets across a folded paper crease and measure a fraction to be taken inside an empty capsule.

Another popular method is to getting a micro-gram scale. In this method, one thing to remember is that the actual weight of a pill is the weight-of-active-medicinal chemical+fillers.

Those are some options. But discuss with your doctor about what method works best for your specific medication. Risperidone should be fine with any of the above mentioned titration methods.