In Meseches Sofrim (18:7) it says that the Minhag on Tisha B’av was, they wrapped the Sefer Torah
In a black cloth, placed it ( Sefer Torah) * on the floor, said Nofloh Ateres Rosheinu and did Kerias Hatorah.
The Abudraham writes , on Tisha B’av you don’t place the Sefer Torah in it’s usual place.(Bimah)
It is very possible from this came the Minhag to place the Sefer Torah on the back of a
person bending down. They didn’t want to put the Sefer Torah on the Bimah or on the floor.
(Shuls had no tables)
*The Tur & Abudraham”s girsa is Tik Shel S.T.
(the Mantel )