3 routes you can go...... or all of them....
1. Not sure what the lever position on the ST4's are like but my 748 was bloody awful. They must have modelled the ergonomics on an Orang-Utang. Unbolt the lever clamp, rip out the retaining/positioning pin and bolt it back up with the lever pointing about 20 to 30 degrees lower. Big difference.
2. Clutch springs. There's plenty of 'uprated' springs around but if you look around I'm sure you can find lighter springs - as long as they don't cause the clutch to drag on release. Trial and error I'm afraid.
3. Aftermarket slave cylinder. Many quote 20 - 30% lighter action but I think that's a tad ambitious. In real life, mine was about 10% lighter.
The biggest change came in repositioning the lever. I had started to develop CTS only in my left wrist, so much so I really didn't relish riding the bike for more than about an hour. After one Surrey ride-out I couldn't physically pull the lever in anymore and had to resort to forced downchanges. Doing the above mods has made so much difference.
Hope you get it sorted.