I usually just lurk, but recently found myself in a similar position with my 36'' corner sink cabinet. Scooping might be an option, but I wouldn't move it any further back. Corner sinks are already set back further than regular sinks and any additional space would be uncomfortable. It would probably also make it hard to reach the faucet. I asked my granite fabricator to put my sink as far forward as possible and it's still 5'' back (I have a 20'' undermount sink).

Don't scoop unless you plan to reinforce the base---a lot. A corner sink base already almost fails the granite support test and scooping weakens the sides even further. You also need ledger support at the back corner for the stone as a matter of course. Your installer should do that automatically, but many don't and need to be told that by you or the granite fabricator.

Go with a standard 25" sink like the base was intended to use. Return the 30" sink or sell it on Craigslist.

Here's our 30" sink in a 25" corner cabinet. The inside edge sits 2-1/4" back from face of cabinet, and I ran cross supports on the other three sides. Our old 30" heavy cast iron sink was installed in the same cabinet for 27 years with no problems.

Here is the framework, I did have to notch out just a bit where the front corners meet the side cabinets.

here is plan view of a 30" sink in a 36" corner cabinet set back 3 and 3/16 from face. Shows how much goes into the adjacent cabinet- if 30" is the inside dimension of the sink.
So what LWO said-do what ctydm did and rebuild the cabinet. BTW that is not a 25" cabinet measurement is take at the wall.

jakuvall, I was measuring the 25" based on the diagonal face frame exposed in front of the sink. If measured like your drawing, mine is closer to 40" or 41"!

ctycdm- I figured that was where you measured, menionted it so someone doesn't walk into HD and ask for a 25" corner sink :)
I use a minimum 39" with a recessed front for a 30", still tight and needs some cutiting but doesn't require the rebuild you went through- a 41 fits if recessed with not work- so 41" for a non recessed sounds right as does what you did.