my client has a thoracic disc with no symptoms is it ok to do back flexion exercises like elefant or spine streatch forward?

I have to assume that you mean they have an injured thoracic disc that is asymptomatic. If this is the case, you will want to make sure that the erector spinal group is strong enough to sufficiently support and control the spinal movements. Remember to get lots of feedback from your client throughout the session to make sure that you are working within their comfort range. Check-in at the beginning of each session to see how they felt after the last session and progress from there.  A herniated disc never heals, so with any client that has one remember that you must always keep the injury in mind.

Does anyone else have a successful treatment plan that they have used when working with this type of situation?

First and foremost, it is important to first check with your client's doctor.

Though I am not exactly sure what you are referring to, here are some tips that may help:

For a bulging disc, a teacher must know which type of bulge is occuring. If if is bulging laterally to the right, then you do not want to do lateral flexion to the left. If it is bulging posteriorly, then you shouldn't execute flexion.

Sonia is correct in saying that more information is needed to properly provide an answer to your question, and please do realize the importance of checking with your client's doctor before continuing any workouts, as their doctor can most likely better detail the situation to you.

Keep in mind that a bulging disk CAN improve and move back into it's proper location with axial elongation and PowerHouse strength.  Therefore as the client improves (symptomatically) movement vocabulary can increase.

As Sonia said, you may wish to eliminate rotation while seated. Initially this would be good advice, but not necessarily all of the time.

We would need to know where the bulge was occurring - is it anterior, posterior, lateral - that changes what you can and can not do.