There is but it's not what most would consider a high ease of use. I use a 3rd party tool call QuickPlan which is available on github at - https://github.com/mgifos/quick-plan
I've been using it for the last 2 or 3 years to coordinate the workouts on mine and my running partner's schedules. You design the workouts in a spreadsheet using some standard notation, then run an import to pull the data into Garmin. It works fine but it was designed by a programmer for personal use so there is no GUI to the UX, if you screw up the notation it can take some time to figure out what you did wrong.
But... it does work and if you're planning a 4 month, 4-5 day a week varied training schedule it beats the hell out of manually recreating the same set of work outs in every person's garmin calendar. And once you 'get' the notation it's not bad.
