XF 1.5 Using PreviewTooltip to display a preview of a post (not a thread)

Using this code will display the PreviewTooltip with the first words of a thread:
class="PreviewTooltip"  data-previewUrl="{xen:if $thread.hasPreview, {xen:link threads/preview, $thread}}"
Is there a way to do the same thing using the last post of a thread instead of the first post ?
I would like to add a PreviewTooltip to the "last post" links on the right of each forum in the node list

I tried editing template node_forum_level_2 and adding the same code but changing the data-previewUrl to /posts/123456/preview but it's not working :( It will work only if data-previewUrl is pointing to a thread URL

If i can get this to work i would also use it in the "latest replies" widget