Bezier or parameterized QEasingCurve

I'm looking into using the Qt animation framework to implement QtWebkit's CSS animations.
As most of the work is done, one thing I can't do is use QEasingCurve.
The reason is that Webkit represents easing-curves as beziers (4 points). The beziers don't translate to the off-the-shelf enum types (unless I try to reverse engineer them), and the customType mechanism is non-parameterized: it's qreal func(qreal), meaning it has to be an absolute formula that cannot rely on dynamic data.
This means that I have to reimp QVariantAnimation::interpolated in order to achieve a simple bezier-curve for the easing!

I'd like us to consider one (or both) of two alternatives:
1. provide an off-the-shelf bezier-curve support in QEasingCurve, something like QEasingCurve::fromBezier(a, b, c, d)
2. have another EasingFunction-like type that's like qreal func(qreal progress, const QVariant & userData), where I can use userData to include something like the bezier's 4-points

Note that this is not webkit specific - if we talk about a future design tool, designers might want to edit beziers by hand and not rely on our off-the-shelf types.