You can customize the default member layout XML file and specify a pattern you want to ignore during the "reorder members" step of a code cleanup.
Have a look at the Type Member Layout section under the Resharper settings. You can see that there already are two exceptions defined for COM interfaces and Structs with the StructLayoutAttribute:
 <!--Do not reorder COM interfaces-->
  <Pattern>
    <Match>
      <And Weight="100">
        <Kind Is="interface"/>
        <HasAttribute 
           CLRName="System.Runtime.InteropServices.InterfaceTypeAttribute"/>
      </And>
    </Match>
  </Pattern>
<!--Do not reorder when StructLayoutAttribute is set -->
  <Pattern>
    <Match>
      <And Weight="100">
     <Or>
        <Kind Is="struct"/>
        <Kind Is="class"/>
     </Or>
        <HasAttribute 
           CLRName="System.Runtime.InteropServices.StructLayoutAttribute"/>
      </And>
    </Match>
  </Pattern>
You could easily create your own IgnoreTypeMemberReorderingAttribute and add a small section in the XML file that check against it.