No more than usual :P
Actually you can go to hell with straps all together! Imagine a yoga ball but one that was moulded to have a big dimple around 6-8 inches deep in one side. You then attach a dildo to the centre of said dimple. Now when you squeeze the sides of the ball the pressure inside is going to push out said dip in a direction 90 degrees from the dual pressure in the sides (so up into a womans va-jay-jay. It may require a little more effort than a spring mechanism but it would be so much easier and quicker to use.
Pictures are on the way!
Behold a wasted 10 minutes!
http://i87.photobucket.com/albums/k151/didxl/questionable%20content/lrg-2-PilatesBallMassager.jpg
http://i87.photobucket.com/albums/k151/didxl/questionable%20content/one.jpg
http://i87.photobucket.com/albums/k151/didxl/questionable%20content/2.jpg
Nice work there diddlexl :)
makes me think of: http://www.lovehoney.co.uk/product.cfm?p=4957
I'd be worried that the dimple would just "pop" in and out like those toys you used to get with shreddies, the little rubber things that you'd turn inside out and they'd jump, usually taking an eye out in the process...
Diddly, your PilatesBallMassager looks suspiciously like one of those ball things they're trying to promote as a substitute for fabric conditioner in your washing machine! I toyed with the idea of buying a pack (£7.95 in Wilkinsons!), but decided the insertion would be too, too painful!
If you made it out of hard enough rubber it shouldn't pop. Or mould it as a dildo using a stong frame. A plastic frame, attached to the ball and covered with the rubber, then the pressure of the inflation would hold it upright. Or just go the whole hog and attach an inflatable ball mechanism to a standard vibrator, just making sure it's well reinforced.
*Returns from shed 1 week later* Success, found just the bit of of plastic, need to put the finishing touches to it though. photo of finished product to follow. (after testing).