Connectives and tags are fundamentally different things, which explains why when we want to use a tag as a connective, we have to coerce it with the CONNECTIVE TAG BO formulation (e.g. .i TAG bo, je TAG bo, .e TAG bo, etc.). Even if we coerced {ca} into a connective, in your example, we wouldn't be much further ahead since we can't connect connectives. (A bit too meta.) We need to find a different approach.
Let's examine the meaning of what you want to say: "even" in this case is carrying a meaning of "one wouldn't expect the main event to occur when the tagged event does, but it does!" so to remark on this, let's just use {ji'a}. {.i vudypai ca lo ji'a sai nu lo tsani ca'o farlu}.
.i mi'e la tsani mu'o