Is it recommended for one for whom congregational prayer is not obligatory—such as the sick and the captive—to prolong the recitation in his silent or audible prayer, like reciting half a juz' in a single rak'ah?

It is recommended for a person praying alone to prolong the standing (qiyam) in prayer, whether it is an obligatory or a supererogatory prayer, due to the Prophet's (peace be upon him) saying: "The best prayer is the طول القنوت (prolonging of qunut)," and al-qunut here refers to the standing. However, it is disliked for a person praying alone to prolong it to an extent that might lead to forgetfulness (sahw).