Well i havent tested precomp0.43 myself but here is a quick tutorial how to.
tho i will tell you the bad side of it beforehand, just so you know!!
precomp0.43 doesnt support stdin-to-stdout support and cls-precomp.dll doesnt utilize in order to make it decompress all in one go, you will spend more time decompressing it but on the other hand you will gain compression on jpg files. with that said i will provide you with a working precomp 0.43 but you will need to make some modifications ..... delete precomp.exe and packjpg_dll.dll from compression folder and inno folders AND delete cls-precomp.dll from inno too. and then replace with this .....
[External compressor
recomp]
header = 0
packcmd = precomp -intense0 -cn- {options} -o$$arcpackedfile$$.tmp $$arcdatafile$$.tmp
unpackcmd = precomp -o$$arcdatafile$$.tmp -r $$arcpackedfile$$.tmp
in both arc.ini inno + compression folders