[ossiblue]

Take if from someone who's had lots of experience with home plumbing, keep things simple and avoid opening up existing connections whenever possible.

Yes, you could make some adaptions under the sink but, if I understand your idea correctly, you'd either have to remove the sink riser shut-off valve to install the T connection and another valve for the shower hose, or you'd install the T in the riser--between the shut off valve and the sink faucets. If you install a T between the supply line and the shut-off valve, that entails removing/installing old plumbing and though your house is only 4 years old, it's rarely a fun or trouble-free job. If you install a T in the riser, then you will need to decide on either hot or cold water to the hose and you'll still have to install a shut off valve in the new T'd line to shut off the shower hose. In addition, any way you choose to do it will require going under the sink to turn on/off the shower hose. Is that practical?

Personally, I'd stick with the hand held shower head for simplicity. If the one you have looks cheap, you may try another make/model.