Using the HighlightManager as suggested by Bas, I'm now able to highlight the elements that I want to:
HighlightManager#addOccurrenceHighlights(Editor, PsiElement, TextAttributes, boolean, ArrayList]]>)
One thing I haven't figured out, though, is how to enable IDEA's F3 functionality (Find Next) for my highlighted elements.
Does anybody have an idea how I can achieve this? Or maybe someone from JB could explain the implementation of the F3 Next action provided by IDEA, in case that would open a (back)door for me.
Thanks for any help. It's the last missing piece I need...