is there any way to disable compiler optimisation for a specific line of code?

No.

Only on a function-by-function basis using the optimize pragma:

 #pragma optimize( "[optimization-list]", {on | off} )

The optimize pragma must appear
outside a function and takes effect at
the first function defined after the
pragma is seen. The on and off
arguments turn options specified in
the optimization-list on or off.

usage:

#pragma optimize( "", off )
.
.
.
#pragma optimize( "", on )