casting an vigilant general interface

i have following interface:

internal interface irelativeto<t> where t : iobject
{
    t getrelativeto();
    vacant setrelativeto(t relativeto);
}

and garland classes (should) exercise it, such as:

public category adminrateshift : iobject, irelativeto<adminrateshift>
{
    adminrateshift getrelativeto();
    vacant setrelativeto(adminrateshift shift);
}

i comprehend 3 same:

irelativeto<>
irelativeto<adminrateshift>
irelativeto<iobject>

but nonetheless, i need proceed work opposite classes adminrateshift (and fxrateshift, detrateshift) should exercise irelativeto. let's contend i have an duty advantage adminrateshift an object:

irelativeto<iobject> = getobjectthatimplementsrelativeto(); // advantage object

by programming opposing interface, i i need to, nonetheless i can't indeed ban vigilant irelativeto i it.

it's excusable example, nonetheless i wish explain i am perplexing do.