The problem with the snippet menu is that you cannot take the callback for selecting - it seems that this is a houdini-internal. So to make it possible, you need to implement one.
Basically every time a snippet is selected from the menu, a temporary callback function runs over the wraglers snippet input looking for channels - similar to the action button for spare parameters, except that these have to be automatically removed/replaced when a new snippet preset is applied.
To achieve this you can customise the buildSnippetMenu() and createSpareParmsFromChCalls() functions in the
vexpressionmenu.py module.
In the hip file below you will find the code. Simply (add) copy and paste the contents into your
vexpressionmenu.py or expand your Houdini path or package. Then go to the type properties of your wrangler, select the VEXpression (snippet) parameter and switch to the menu tab. Replace the following code and apply:
import vexpressionmenu
node = kwargs['node']
snippetname = 'attribwrangle/snippet'
parmname = 'snippet'
return vexpressionmenu.custom_buildSnippetMenu(node, snippetname, parmname)
For debugging or in general I would recommend a HDA wrapper around the wrangle. So use it at your own risk!Now, every time the snippet provides a channel, the corresponding parameters will be generated.