Many years ago we did extensive studies on the affects of soft water on plants, and the results were exactly as expected. Some plants are affected, most are not under normal hardness conditions. We have even done studies on softener waste distribution onto lawns to see what the affects were. Most lawns were not affected, some were killed. Soil type has a lot to do with it. I had a customer draining his softener onto his backyard for 20 years, his lawn was just fine. All this being said...
Make an effort to bypass the irrigation, even if it will take some time. Cutting concrete and repairing it is not that difficult nor is it overly expensive. You can rent the cutter from Home Depot or the local rental yard for a reasonable price. If your palm trees or plants are priceless, then use extreme caution. If your house is on a raised foundation, then bypassing the plumbing should be fairly easy. If the plants start to show problems with the softened water unlikely but possible), then you can always bypass the softener at the bypass valve when you water the plants. You can also set up a very simple solenoid bypass that is actuated from your irrigation controller. Let me know if you need more information on this.
Let us know what you decide.