Is it permissible for the Imam to face the Qiblah and for the congregants to stand in their places, raise their hands, and offer silent supplications after the sermon for rain (Khutbat al-Istisqa')?

The rain prayer (Salat al-Istisqa) is valid if the congregants (ma'mumun) are sitting and the imam is standing, and it is sufficient. However, the Sunnah is for the congregants to sit and the imam to stand. Scholars have differed regarding whether to vocalize (jahr) or supplicate silently (israr) during the supplication (du'a'). Some prefer vocalization, like the Malikis, while others prefer silence, like the Hanbalis. Still others, like the Shafi'is, see a distinction: vocalizing when facing the people and supplicating silently when facing the qiblah. If the imam vocalizes the supplication, the congregants say "Ameen." If he supplicates silently, they supplicate silently to themselves. It is authentically reported in Sahih al-Bukhari that the Prophet (peace be upon him) raised his hands, and the people raised their hands with him, supplicating. In another narration, he vocalized the supplication.