How does one pass xacro blocks as arguments in a launch file?

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The insert_block feature in xacro is super nice. However, I am not quite sure how to pass such a block argument from a launch file. Most of the answers I have seen so far are about passing single arguments from a launch file. Here is what I am trying to do:

<xacro:macro name="foo" params="*foo_block">
   <link name = "foo_link">
     <xacro:insert_block name=foo_block />
   </link>
</xacro:macro>

And in the launch file, I would like to load the xacro to a parameter like this:

<param name="my_param" command="$(find xacro)/xacro --inorder '$(find my_package)/urdf/foo.xacro' foo_block:=??"/>

Any help on how to do this is very much appreciated. Thanks!