That is already supported: Select the label of your group node, go to the properties table in yEd's lower right corner, enter the text "2 22 2 2" (that twenty-two is not a typo) for property "Insets".
The first number is the inset from top, the second the inset from left, the third is the bottom inset, and the fourth the inset from right.
No text means "use default insets" which is the same as "2 2 2 2".