Sounds like you have the problem well in hand.
Here is something else to consider.
Billet extended clutch arm.


You can get a YZF450 (Quad) clutch arm (About 20 or less on eBay) and a Billet arm for the YZF450 clutch arm on ebay for about 30.
Remove the clutch arm from your 500.
Cut the top off your KX250/500 clutch arm removing the lever part completely.
Then, cut the top of the YZF450 clutch arm off leaving about 1/4" of the shaft on it.
Weld the top of the YZF to the bottom of the KX250/500 clutch arm.
Install on your bike and enjoy about a 20% easier clutch pull with no hydraulic clutch.