Not sure if I understand the question but I'm assuming you want a "sweeter" Blueberry without using any Creams?
Blueberry Jam probably uses 5 pounds of sugar so...
The problem is with the normal sweeteners we use for DIY, Sucralose or Stevia you may get some aftertaste if using too much.
Don't think I'd use EM cause it's just gonna mute the Blueberry.
FA Meringue and Custard both have a hint of Lemon that helps the Blueberry a bit, but Meringue is a bit sweeter IMO.
Tiny amounts of Maple Syrup or Molasses may work but it might taste more like Pancakes or Waffles, (0.5% or less).
Other thoughts, 0.5% CAP Golden Pineapple, OR, 0.5% CAP Sweet Tangerine.
Think of using other sweet type fruits like using spices, just a tad of "this and/or that".
If kept low enough you won't really even taste them.
TFA Blueberry Wild 5%
TFA Brown Sugar 3% (might be too dark for Jam IDK for sure)
FA Meringue OR FA Custard 1%
Sweetener 1 drop in 15ml (optional)
OR
(If Brown Sugar is too heavy/dark)
TFA Blueberry Wild 5%
FA Meringue OR FA Custard 1%
Stevia or Sweetener 1-3%
Other Blueberries like FW and CAP seem to be not quite as sweet but some like the flavors better.
I don't have anything like a Blueberry Candy flavoring around...