I found where it is possible to disable the squiggly-line; but,
unfortunately, setting it to highlight instead does not seem possible.
The setting can found here:
window->preferences
|-General->Editors->Annotations
select "C/C++ Index Markers" from the "Annotation Types" listbox
Uncheck the "Text as: ..." checkbox to disable the squiggly-line.
... but a slightly more preferable option may be to choose a different
color for the squiggle (I found a color to my satisfaction by reducing
the saturation value of the default color).
Not a solution, but I hope that helps.
Cheers,
~Andrew~