Assign atlas texture to button in lua?

[LudiusMaximus]

OK, that's an idea.

But let me ask differently.

How can I achieve that the highlight Texture texture is shown as big as the normal Atlas texture?

XML:

<NormalTexture atlas="QuestCollapse-Show-Up"/>
<PushedTexture atlas="QuestCollapse-Show-Down"/>
<HighlightTexture file="Interface\Buttons\UI-Common-MouseHilight" alphaMode="ADD" setAllPoints="true">
  <Size x="48" y="48"/>
  <Anchors>
    <Anchor point="CENTER"/>
  </Anchors>
</HighlightTexture>

Lua:

myButton:SetNormalAtlas("QuestCollapse-Show-Up")
myButton:SetPushedAtlas("QuestCollapse-Show-Down")
myButton:SetHighlightTexture("Interface\\Buttons\\UI-Common-MouseHilight", "ADD")
--???