We managed it with oLark.
oLark is a good chat client with a nice API but it required a chunk of custom development back when we did it about 18 months ago.
Here is some of my code I've shared (not the complete solution, but a way to get lead data into Javascript)
https://github.com/mozz100/marketo-whodatI would recommend oLark but unless you are confident with coding, you're restricted to what's on Launchpoint...