JsonSchema Array of mixed items in fixed position with only second item required

I need to define a Json Schema which accepts an array. This array can have one of the following structures:
1: ["StringConstant",{someKeys:someValues},"StringConstant","StringConstant"]
2: [{someKeys:someValues},{someKeys:someValues},...]
3: ["StringConstant",{someKeys:someValues},"StringConstant","StringConstant","StringConstant",{someKeys:someValues},"StringConstant","StringConstant",...]
4: ["StringConstant",{someKeys:someValues},"StringConstant","StringConstant",{someKeys:someValues},...]

The StringConstant are all the same and the Objects {someKeys:someValues}all have the same keys.

Basically the Object {someKeys:someValues} can stand on its own or with a leading StringConstant and two trailing StringConstant

Currently I have:

{
 "type": "array",
 "items" : [
      {
       "const": "first"
      },
      {
       "type": "object",
       "properties":{...}
      },
      {
       "const": "second"
      },
      {
       "const": "third"
      }
    ],
 "additionalItems": false       
}

But this schema requires the constants to always be present.
Is there a way to define and validate the required structure with JsonSchema?

One possible way I found is to define the array objects as anyOf and write the validation for the leading and trailing constants myself.