One of the important aspects of the Discovery Bible approach that we are using is to methodically include an encouragement & challenge to tell others in each session. This is usually towards the end of the session with a question like 'who do you think you might tell?' or 'how / when might we tell this to others?'.
This question is used even in the earliest stages, before the participants have received Christ for themselves. The fact that they have not made any kind of decision for Jesus doesn't mean that they can't start telling others of what they have discovered so far, or of their steps of exploration.
This is important because it builds in the principle that we can share our faith right from the start. The Great Commission is not some add-on for the few keenies, but fundamental to following Jesus - to discipleship itself. To talk of 'missionary disciples' is counter-productive because true discipleship should be intrinsically missional by definition - it doesn't need the adjective!
At the start of the next session in amongst the natural 'how are you?' questions, each person is asked how they have got on with telling others. Of course this is not an interrogation, and we don't do shame, but we do model loving accountability from the outset - which is another key component of the approach.
Of course it may be that someone has not identified any opportunity to tell, or not seized it when it presented. But with the Spirit at work pleasant surprises can arise: in one session someone fed back that they had not just told the one person they identified the week before, but in fact had told the whole group that they were mutually part of. It is this one-to-many occurrence that gives rise to the possibility of gospel multiplication and further spread of the Good News.