How to abbreviate section name in table of contents?

I have a couple of long section (Heading 2) names, and I’d like them to show up differently (I.e. abbreviated manually) in the table of contents. How can I specify alternative text for some sections, which gets used only in the table of contents?

Short answer, you can’t:

Bug 37307 - Fields for very long titles don’t allow the use of reduced versions in TOC

Long answer, you could, but you’ll need some heavy workarounds like using a “fake heading” paragraph style displaying the long text and the real heading applied to the short text, which will need a character style (white, small font, so it’s not printed) on top to “hide” it. Maybe it’s easier to rephrase your heading: any workaround for this issue will have its share of problems.