Increased tone in muscles following hemiplegia is often adopted by the client attempting to achieve a functional goal to compensate for a lack of tone and movement or stabilty in another area. A problem solving approach must therefore be adopted to find out the underlying cause of this hypertonicity. Often by giving the client the stability or movement they are lacking elsewhere (possibly more proximally) they can then use their limb more selectively rather than having to recruit the muscles for stability.
Working for eccentric lengthening of the hypertonic muscles as well as working the antagonists may also assist in reducing the 'spasticity'. Splinting may help to lengthen the muscle but I feel it's important to work out why they are having to recruit the tone in the first place.