I have added this functionality to the following branch:
https://github.com/timbrown5/parameterized-remote-trigger-plugin/tree/JENKINS-22384-Add-EnvVars

We are using this locally, please let me know if you'd like me to submit a pull request.

Note: This branch also has a workaround for some local networking issues we are having. We are finding that sometimes a connection drops and this makes the plugin drop out too early. To workaround this I have added a connectionRetry section to sendHTTPCall (in the catch IOException) that retries the call x amount of times before failing - suing recursion. This is hard coded to 5, but could be available to be configured via jelly input (although we've only ever seen it retry once at a time).

Added this code to the master branch in my fork:

I have added all of the below EnvVars (they all get added in one method, so it should be easy to extend/change in the future):

• LAST_TRIGGERED_JOB_NAME="Last project started"
• TRIGGERED_BUILD_NUMBER_<project name>="Last build number triggered"
• TRIGGERED_JOB_NAMES="Comma separated list of all triggered projects"
• TRIGGERED_BUILD_NUMBERS_<project name>="Comma separated list of build numbers triggered"
• TRIGGERED_BUILD_RESULT_<project name>="Last triggered build result of project"
• TRIGGERED_BUILD_RESULT_<project name>RUN<build number>="Result of triggered build for build number" <-- I have implemented this one has underscore near the run, e.g.: TRIGGERED_BUILD_RESULT_My_Project_RUN_12 instead of: TRIGGERED_BUILD_RESULT_My_ProjectRUN12. According to the Parameterized Build plug-in documentation this is wrong, but I think this is easier to use. Can change be changed easily if required.
• TRIGGERED_BUILD_RUN_COUNT_project name>="Number of builds triggered for the project"

Tim, when you think it's ready please go ahead an issue PR.
And this entire plugin is lacking unit tests

I think it would be best to fix the major issues and add UTs before we try and put this in (as it could cause a lot of confusion).

I can create another branch here and submit some of the UTs I have done - at least it will be something to build on .

After revisiting this today I released that using the same EnvVars as the Trigger Build building will lead to conflicts (we will be overwriting each other's Env Vars). Renaming the Variables to:
•- LAST_REMOTE_TRIGGERED_JOB_NAME="Last project started"
•- REMOTE_TRIGGERED_BUILD_NUMBER_<project name>="Last build number triggered"
•- REMOTE_TRIGGERED_JOB_NAMES="Comma separated list of all triggered projects"
•- REMOTE_TRIGGERED_BUILD_NUMBERS_<project name>="Comma separated list of build numbers triggered"
•- REMOTE_TRIGGERED_BUILD_RESULT_<project name>="Last triggered build result of project"
•- REMOTE_TRIGGERED_BUILD_RESULT_<project name>RUN<build number>="Result of triggered build for build number"
•- REMOTE_TRIGGERED_BUILD_RUN_COUNT_project name>="Number of builds triggered for the project"

Thanks Tim, this is a very useful feature. I have tested it and it works well.
It would be nice to see it in official version.