Right hander: ball has pin under middle finger and CG "slightly" to the left but not as far as to the ball track. So it should have slightly "negative" side weight? I like the ball shape and reaction I am getting but I can tell about 1/3 to 1/2 of the width of the ball track is over the thumb hole.
Could a weigh hole help? and where should it be placed? Possible to have one on the left side( unlike common ones on the PAP side)?

My driller suggests a hole about 3 inches to the left of the grip center( to give it some "positive" side weight). Does that sound right?

I am a little worried because after that it may roll over the weigh hole? I may try to drill one about an inch below what he proposes and that should give a little more surface for the ball track.

Higher track bowlers have a more difficult time keeping the track off the thumb. Lower pin placements usually lower your track bow tie. I'm a lower track bowler and never have a problem with pins around my middle finger, either above or below. I have a guy I do ball work for that tracks high and when he tries to use my stuff that's drilled pin above or below middle finger, he always hits the thumb hole. I tell him to try to get his hand off the side more and the track moves down off the thumb, but he has to make an effort to do so. Is the ball over-flaring? What is your pap? When I place the pin around my middle finger it's about a 4-1/2" pin to pap and my friend that uses my stuff has a pap of 5-5/8" over and so the same ball for him ends up being over 6" pin to pap. I try to keep his pins no further left than the center of the grip center line, which ends up being around 5-1/2" pin to pap. Your driller needs or should know you pap and the safe zone to keep your pins. I would say a lower weight hole may help, but I think the layout is the main cause! Just my $.02, Bruce

For starters you've placed the pin too close to the track, which is one of the controlling stable points in a bowling ball (track, positive & negative axis) which translates to it will pull the track towards it...generally up on the thumb. Secondly a weight hole is based upon your positive axis point not referencing static weights other than per USBC regulations....so a weight on the negative side of the track will literally do nothing
I would suggest drilling the middle finger deeper to give it positive wright then add a hole down your VAL to raise the bowtie plus increase the flare so it flares off the thumb quicker