Is it possible to measure your sit bones at home? Some bike shops have gel pads that you sit on to measure the distance between your sit bones. Is it possible to take this measurement on your own at home, or does this really require special-purpose equipment?

[Related question: Should I use a narrower saddle on a road bike than I would on my hybrid commuter?]
Copied this from a BikeRadar article:

How to measure your own sit bones
Of course the measure you really want is between the centres of your ischial tuberosities – the pointy lower parts of your pelvic bone on either side. Many bike dealers have a pad that you can sit on to measure this distance, but you can do it at home too.
Take a piece of aluminium kitchen foil and place it on a carpeted stair. Sit on the foil, lean forward a bit to approximate your riding position, then lift your feet. This should leave a good impression of your rear in the foil, and you can measure between the two points of deepest impression to get your sit bone width.
‘Narrow’ sit bone width would be 100mm or less, medium 100-130mm, wide over 130mm.
A saddle’s width is measured from edge to edge across the top, and Specialized recommends a 130mm saddle width for narrow, 143mm for medium and 155mm for wide. These ﬁgures should translate approximately across other ranges, with all other factors taken into account.