Tom
Agreed, the LIE service rd. is not as scenically interesting as taking assorted side roads to the north.
BUT, that adds a ton of mileage, as well as being extraordinarily convoluted.
I regularly ride Old Country Rd. and Manor Hill Rd up to E Northport, and then routes east and north to the Sunken Meadow/Kings Park area, but to get further east you have to use Rt25a for a bit and get around Smithtown and that road (Rt 25A) SUCKS for bikes. And I do not know the area east of Kings Park and north of the LIE as well, other then the section I described around Lake Ronk - which was part of the High Point Century 20 years ago.
The suggestion would be then to peruse the Suffolk Bike Riders cue sheets -
http://www.bicyclelongisland.org/sbrafram.htm and try to find a route east along the north shore.
Note that heading north and then east of the LIE probably adds 20 additional miles to the route, putting it into the century range, that choice is up to to the OP.
Steve B.