So in short the easiest (if not best) method to get away from the ridiculous haste stat weights simc gives you would be to just sim for an ultraxion type fight (never simed patchwork anyways), while the best would be to sim for the specific fight in question, change some items and sim again (and again) and just consolidate the values you get?
/edit: Or is there a way to modify boss uptime in simcraft? Haven't found any in the options at least, but I'm not all that familiar with the html commands