Got a response. We need to run this code, perhaps in a console application. I still have not figured out how to remove the event handler when it was added, though ...
string siteUrl = Console.ReadLine();
SPSite site = new SPSite(siteUrl);
SPWeb web = site.OpenWeb();
string listName = Console.ReadLine();
SPList list = web.Lists[listName];
string assemblyName = "Issue.EventHandler, Version=1.0.0.0, Culture=Neutral, PublicKeyToken=89fde668234f6b1d";
string className = "Issue.EventHandler.IssueEventHandler";
list.EventReceivers.Add(SPEventReceiverType.ItemUpdated, assemblyName, className);
source
share