How do you prompt a tree to drop some/most leaves?

I live in a dense suburban area and I have a line of maple trees ( from 6" to 12" in diameter, 30'-40'? feet in height) on the southern property line that do a lot to shade the southern exposure of my garden. Ideally, I would like to have a tree trimmer come in and coppice these trees, as I would like to have some shade in the garden just not 75% shade, but I do not want to spend the money to hire the trimmer and I'm not comfortable with heights or chainsaws and certainly not in conjunction (and there is a powerline underneath them which complicates matters for me, as well as a shed and garage nearby).

So, instead of coppice/trim, I was thinking of girdling the trees but that would kill them altogether and that's not exactly what I'm looking for; I thought I might girdle them at 15' and maybe they would survive, but the wood above 15' feet might become a hazard in a few years, and it wouldn't likely affect the amount of leafing/shade this year.

My current thought would be to create a major pulse to the trees by digging a 3 foot trench around the trees, which might limit their ability to pull in water this year, and I'm thinking/hoping, might cause leaf drop early.

Does anyone think this will work? Are some of my other options perhaps preferable? Are there options I haven't considered?

I'd call the power company and tell them you are "worried about the lines" and see if they will trim the trees. Might work...