How to perform a Get/put on contract with composite key

I'm able to do a get on the trans using query parameters
https://{{URL}}/api/Trans?BT_ID=1399950&product_code=LASTAR2013/STAR&ST_ID=1399950&Date_Entered=2013-01-28

But the identity element of the response is a composite key

            "IdentityElements": [
                "1",
                "1",
                "1170269"
            ]

I've tried several different notations to do a Get by this key

https://{{URL}}/api/Trans/1/1/1170269
https://{{URL}}/api/Trans/1&1&1170269
https://{{URL}}/api/Trans/1:1:1170269
https://{{URL}}/api/Trans/1¶1¶1170269

without luck. All the examples of put use the id of the record in the URL. Is there any way around this issue to do put's on records with composite keys?