Treat writing as part of your job.
Many academic writers see their writing as something to be done after hours, as an add-on, once they have finished every other duty. It is extra work for vacations, weekends, evenings, breaks. I propose that you see writing as part of workaday life. In fact, you could work from 8-5 five days a week and incorporate writing into that day.
If your contract says you should be spending 40 per cent of your effort on research, that should apply to your daily routine as well.
If writing is not truly part of your job, and actively discouraged, you should still treat it as part of your job. Just fuck'em.