This article is from the comp.sys.acorn FAQ, by Paul Vigay with numerous contributions by others.
Solid drags are controlled by bit 1 in byte 28 of the CMOS RAM. Setting this bit enables solid drags on all solid drag 'aware' applications. However setting this bit using a *FX command from the command line is a foolish way to do it, as this will unset/set the other 7 bits in that byte which have meaning to FileSwitch and the Wimp. Accordingly the recommended way to set this bit is using a program like this BASIC one enclosed below :-
REM Toggle state of DragASprite bit in CMOS REM Read byte SYS "OS_Byte",161,&1C TO ,,byte% REM EOR byte with mask for bit 1 byte% = byte% EOR %10 REM Write byte back again SYS "OS_Byte",162,&1C,byte% END
Which safely sets bit 1 while preserving the settings of the other bits.