Ran through this with Steve and he said you would never weld it strong enough to stand all the torsional stresses, he said if you do, go ahead but if it snaps which is likely it wont just drop off the rod..he chuckled a bit then said ok just dont go into what could happen its just a no go idea.
You have to take into account with a shock thats made for a certain bike the linkage rates and swingarm length which produce different leverage effects on the shock which is then valved for to take these factors into account. Also the shock for the R6 is valved for a faster bike which loads spring differently due to the swingarm and tie bar lengths. In fact you would want a lighter spring to account for this.
If it worked well then why dont Ohlins make a generic fitment shock or why dont any minitwin racers on a budget use a GSXR or ZX6 one?.
If you want to change one on the cheap then at least go for one that fits. Or foresake a few days on track for one that will work for your bike.
being a racer i know which option id go for...the one that helps me to make the most from my bike and make alot more than a few tenths. Having ridden a bike with a ZX6 shock i assure you one built for the job is worthy of a year trying to make tenths
