Ways to combine Shimano M-615 SGS with 9-speed cassette and shifter current setup is Shimano M-615 SGS rear derailleur, Shimano Deore M591 shifter and Shimano CS-HG81-10 11-36T cassette

My idea is to return to 9-speed while not throwing the derailleur. Wanna change the shifter to SunRace M95 (9sp shimano compatible, dunno if pull ratio should be changed to be DynaSys compatible) and some 9sp cassette with alu spider (the hub has alu freewheel body) or at least to remove one of the cogs.

Any ideas if the 9sp shifter will work with the 10sp derailleur? Thanks in advance
Shimano 9 and 10 speed mountain stuff have different cable pulls. 

So, if you want to use a Shimano 10 speed mountain  derailleur in a Shimano 9 speed setup (i.e. 9 speed shifter + cassette) you either need to:


Buy a friction shifter, which obviously doesn't care about the speeds
Buy a device which can change the cable pull appropriately (in this case, a JTek Shiftmate 6 would work) and use a Shimano-compatible 9 speed shifter. Note that this will likely cost more than the 9 speed derailleur. 


10 speed cassettes in a 9 speed system introduce another level of complication since the cogs are a different distance apart, and would require a different adjustment to cable pull. It'd be like you cascaded a JTek Shiftmate 2 and 6.