Using predicates on k2 fields

I'm trying to show the last value in a multi-value XML field and it is not working (my terminology might be off, this is new stuff for me). Example XML:

<sodas>
<soda>
<name>Coke</name>
<isCaffinated>Yes</isCaffinated>
</soda>
<soda>
<Name>Sierra Mist</name>
<isCaffinated>No</isCaffinated>
</soda>
...
</sodas>

If set the xpath on a k2textbox to name using the dialog, I end up with:
/ns1:sodas/ns1:soda/ns1:name

This sets the field to the first node (Coke), but what I want is the last node. So I change it to this:
/ns1:sodas/ns1:soda[last()]/ns1:name

I think my syntax is OK, but it does not work. The field is blank.

Any ideas on how to do this? I'm fine with just using a regular text box and setting the value in the PageLoad, but I don't know how to bind to the XML data (or how to loop through it).

Any ideas?