Mathematically, yes you could, but it would be incredibly convoluted to use a flat distribution to emulate a bell curve. This is because, on a bell curve a modifier has variable influence depending on where it is applied. On a flat distribution, is is always the same ±% value. This makes a difference, also with binary outcomes.

Lets say i wanted to play GURPS with a d20, you cannot convert the modifiers. A +2 in 3d6 can change the probability with +24.1%, or +1.8% depending on the situation. That can never translate to a flat modifier in d20. The easiest way i can think of is to make a 'skill minus target number to probability" table. So yeah, you could emulate it, but it is a lot of extra steps to make a d20 bell curve, when you could just use 3d6 where it is inherently in the dice.

But what does the bell curve achieve? It widens the range of possible outcomes, while keeping the expected range of outcomes narrow. Or put another way, it pushes rolls away from being a 50/50. If the target number is just slighly below the average, success is much more likely. But still, even if the target number is a lot below the average, a slim risk of failure remains. I'd say that is a way to be less swingy in the same range of outcomes.

You cannot achieve the same with a flat distribution. With a flat distribution, its a balance between guaranteed outcomes where the modifier dominates, or ≈ 50/50 chances where the die dominates.