How do I insert data from a custom node poller into an alert?

I created a custom node poller to pull hrSystemUptime from a MacAfee web gateway proxy server.  This variable is to replace the uptime that SolarWinds uses.  The uptime SolarWinds uses is wrong, it sends reboot alerts when we simply load new policies into the proxy server.

hrSystemUptime does a better job for us, and I used it to improve the quality of the reboot alert.  So this is all good.

Now I need to push this new hrSystemUptime variable into an external system.  I'm using a json post to do this.  My json posts are working great, so nothing to discuss there.

When I use the "INSERT VARIABLE" function on email editor under the trigger actions screen, I see these two variables offered by the variable picker when I search for custom values matching hrSystemUptime:

${N=SwisEntity;M=CustomPoller.MIB}
${N=SwisEntity;M=CustomPoller.UniqueName}

When I insert these, I see this on the output:

HOST-RESOURCES-MIB:hrSystemUptime
hrSystemUptime

The first line of the output should have been an integer value "494242039", not the string "HOST-RESOURCES-MIB:hrSystemUptime".  

How do I insert an integer value from a custom node poller into an alert?  What am I doing wrong?