define vspackage in multiple vsct file

Question

I have a vspackage that I want to define in multiple vsct files. So for example, I have 2 buttons under the same package but i want to define the 1st one in a.vsct and the second in b.vsct. I tried

a.vsct:

...
<Commands package="guidMyPkg">
<Button guid="guidMyCmdSet" id="cmdidMyId1" priority="0x0000" type="Button">
..
</Button>
</Commands>

b.vsct:

<Include href=a.vsct>
...
<Commands package="guidMyPkg">
<Button guid="guidMyCmdSet" id="cmdidMyId2" priority="0x0000" type="Button">
..
</Button>
</Commands>

am I doing this wrong