I will talk big and vague in meetings about what I've accomplished. I'll talk about why what I'm building turned out to be more complicated than thought originally, and will take more time than allotted. If necessary will build interfaces that look like I'm doing the work when in fact I'm not.
Keep in mind, I don't do this maliciously to "steal" from the company. I do this because I have a certain amount of creative energy, and sometimes the well just runs dry. I can't think about complicated things (much of my job is architecting systems) and I have trouble focusing. Instead of pushing myself to burn out further, I understand it as part of a boom/bust cycle and take a break at work. Sometimes this lasts up to a week (even more in a few cases).
Then one day during the bust, I'll get the wind back in my sails and start up again.
This happens once every few months, although sometimes it can be triggered by a larger project. Sometimes I'll allot a week for something, not do anything on it, and then complete it all a day before it's due. When I say "not do anything" I mean I'm not actually coding, however I think my subconscious is mulling the problem over and I'll have an "AHA!" moment when needed.
Really, it helps to get good at bullshitting and buying yourself time. Practice, practice, practice. Once again, not maliciously, but for your own well-being. Pad your days out when giving estimates to people.
Hope that helps/is applicable to your situation.