It can be done. Just need to be very paranoid while doing that. I once worked for a big company where I got roped into security/loss/fraud prevention, and if they got a whiff of fraud they'll go to some length to catch you at it.

LTD for lower back issues? Those telephoto lens shots of you playing 18 holes will probably get you canned.

True there are a lot of conditions which have subjective symptoms and can't really be confirmed or denied by a doc. The problem with most of those is that you may not be able to convince the FAA that you're all good as soon as you're ready to come back to work. That game works better if you're just "retiring" early.