help on loop variables

As far as I can tell, it is impossible to use $varExists() inside a
loop variable. So I'm asking for help on how to re-think my situation.

First, here's what will not work in Cheetah. varExists is always false:
#for $row in $here
  <tr>
  #for $cell in $row
    #if $varExists('cell.isHeader') and $cell.isHeader
    <th style=3D"$cell.style.inline">${cell}</th>

Second, here is a similar template, but written in SimpleTal that does work:
<metal:block tal:repeat=3D"cell row">
    <th tal:condition=3D"cell/isHeader"
           tal:attributes=3D"style cell/style/inline;
           tal:content=3D"cell"></th>
</metal:block>

I have some table cells with a varying suite of attributes; where
those attributes exist I want to use them, and of course I don=92t want
to get an error when trying to use a non-existent attribute.

Finally, my question:
is there any way to accomplish this with a Cheetah template?

thanks,
--Tim Arnold

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