how do i use AB test with go-kit

[zhangweiii]

i want test user use serviceA1, and normal user use serviceA2

type Endpointer interface {
	Endpoints() ([]endpoint.Endpoint, error)
}

this interface ignore meta info, and

type Balancer interface {
	Endpoint() (endpoint.Endpoint, error)
}

Balancer ignore request info, so how do i use special service by request