While the Rolling Stones continued to build a huge live reputation (at home and abroad) and at the same time became more confident in the studio, manager Andrew Oldham occasionally took them away from their blues and R&B roots, and recruited members of the band, including Stu, for his own Andrew Oldham Orchestra. As mentioned before, there was no actual orchestra per se. The orchestra's name was applied to recordings made by Oldham using a multitude of session musicians, including members of the Stones.
Oldham's idea of capitalizing on the Stones' success by issuing some 'experimental' Jagger-Richards compositions to unsespecting artists was not exactly a commercial success. During the so-called 'Sleepy City' sessions at Regent Sound Studios and Decca Sound Studios, London (June 29-July 7, 1964) recordings were made for the Rolling Stones, the Andrew Oldham Orchestra and Marianne Faithfull. With Andrew Oldham producing, several tracks were laid down by a basic group comprising of Mick Jagger, Keith Richards and Ian Stewart, with additional session musicians like guitarists Jimmy Page, Big Jim Sullivan and John McLaughlin helping out.
One Jagger-Richards track, (Walkin' Thru The) Sleepy City, was given to British band The Mighty Avengers. Predictably it flopped. The Stones' own version of the song is ruined by being over-produced. Simplicity, as they would soon learn, was the key to success. Of course one wonders if Stu felt comfortable with his piano playing on the Orchestra tracks. I don't know, but I doubt it.
Adapted from the following source: Martin Elliott, The Rolling Stones. Complete Recording Sessions 1962-2002, Cherry Red Books, 2002.