In Awesome <3.5 I did it that way:
mytasklist[s] = awful.widget.tasklist(function(c)
local task = { awful.widget.tasklist.label.currenttags(c, s) }
return '', task[2], task[3], task[4]
end, mytasklist.buttons)
But in 3.5 that doesn't work anymore as in 3.5 there is no such function - awful.widget.tasklist.label.currenttags() and new function awful.widget.tasklist.filter.currenttags() returns just true or false so its not the real replacement.