While I completely agree with ivansc and so I do NOT recommend to use the following, you can install:
https://www.xlutop.com/buzz/zip/dxshell_v1.0.4b.zip
Just copy dxshell.dll and dxishell.dll to your VST folder.
Note that you need these files and not (!) x64 files. So the chain will work as DX (32bit) -> VST (32bit) -> (REAPER own bridge) -> REAPER (64bit).
I repeat, if you really need 32bit DX with 64bit VSTs within one project, running REAPER 32bit and so bridge 64bit VSTs is probably more stable then above solution.
Also note that DX FXes with side-chain support are crash prone in REAPER.