I was able to do this. You’ll need to use C++.
if (const auto Widget = NewObject<UUserWidget>(this, EffectTooltipWidgetClass))
{
if (const auto Tooltip = Cast<UEffectTooltip>(Widget))
{
Tooltip->SetEffectInformation(
InGameplayEffect->GetDisplayName(), InGameplayEffect->GetDescription()
);
SizeBox->SetToolTip(Cast<UWidget>(Widget));
}
}
There’s no way of doing it currently in blueprint.