I have read enough AAIB reports of CFIT that would put me off going below MSA without being VFR. Remember that MSA figures exist for a reason!
If you must go below MSA, I would use a nearby airfield with a published approach, once VFR, break off and do what I like below MSA but of course abiding by the low flying rule. Or I would go over the sea, and descend to what I deem is safe (not normally below 1000ft).
The real question is why would you want to descend below MSA without being visual? You normally start to see through the lower parts of the clouds when you get close to the cloudbase, you would still be well above the low flying rule when fully VFR if you continued to descend a further few hundred feet or so.