Hmmm i doubt there will be a useful way without taking off the clutch cover and stripping the clutch down and cleaning the plates with brake&clutch cleaner. it will be combo of old oil, weakened or rusty clutch stings and potentially corroded steel plates. honestly with some basic tools and cheap parts (MZ bits aint expensive) i know ost2rad do a refurb setup to do a complete clutch for your bike for £45 ish (59 euro)
http://www.ost2rad.com/Complete-offers-Sets/Repair-set-clutch-MZ–TS250–1–completely.html
Other things to consider is, if the bikes sat a long time it may need crank seals doing, and carb cleaned, tank drained, cleaned and fuel tap. 2 strokes don’t like being sat unused, its probably the worst thing for them, also check the points, charging system etc. I am sure other more knowledgable members will come along and correct any mistakes I’ve made in my reply. I’ve only ever owned 2 MZ,s but have rebuilt a few small jap strokers, and restored a few old bikes that have lain for years.. the issues to them are common from lying unused. first rule is always a thorough clean of fuelling system, and make sure you got compression and spark. It will save you endlessly chasing issues. Hope this is of some help to you.