I don't think it is possible to achive that with a single-row card. If it is, it's probably by using a DAX formula similar to the one described in the following link(But I think it could only be achieved by dynamically generetaing row indices, which is probably imposible in DAX):
http://sqljason.com/2013/01/group-multiple-rows-to-single-delimited.html
I think the best solution to your problem would be either writing your own custom visual or modifiying the single or multi row cards to do that.