How to make agar less brittle
It doesn't seem like you can get a soft, elastic gel using agar, Modernist Cuisine lists an elastic one but classifies it as firm(4-140):

Texture     Firmness    Gelling Agents       Scaling
----------------------------------------------------
Elastic     Firm        Locust Bean Gum      0.15%     
                        Agar                 0.10%
                        Xanthan Gum          0.20%


Although, they do have an elastic gel in the coating gels section that is classified as tender (4-151):

Texture     Firmness    Gelling Agents       Scaling
----------------------------------------------------
Elastic     Tender      Sorbitol             3.00%     
                        Agar                 0.60%
                        Xanthan Gum          0.25%