Dear Gopal,
There are a few suggestions,
1. It may be appropriate to invite his wife, if possible other family members-son(s), daughters and ask them to be on the stage to appear together with the retiring employee;
2. If so say few pleasant things about the wife and other family members, how they are placed and wish them well and very best, good health and present them with bunch of flowers or shawl (being in Bangalore a Mysore turban) ; If need be the wife also can be asked to say a few words, if they are willing and able to speak;
3. Actual words of a farewell speech would depend on the nature of duty and his contribution and if you are eloquent to give good speeches you would know how to make the function memorable one.
4. May be you can include remembering/recalling a particular event or occasion in which the retiring person impressed you all, which may be fitting for the occasion;
5. I hope you would be preparing to present him with a memento or a purse/gift. If so you may add a few words signifying why you chose such a gift which considered most appropriate for him.
6. Also express your sincere apologies for inconvenience, if any caused to him during his service.
7. It may be fitting if you are able to present a cheque of his full and final settlement/gratuity, Service certificate together with a special Appreciation Letter, on the occasion itself and/or if he is eligible for pension or a parting gift from the management, you may present it's orders/gift cheque;
8. It's also very much fitting that few of you can accompany or drop him(them) in your office car at his house and depart after sharing a tea at his house;
9. Also add a few words meaning he shouldn't think he is 'out of office' from the very next day, but always welcome to visit them as much as possible;
10. You might as well host a high tea (if in the evening) or a lunch or dinner followed with a group photo, which copy should be sent to his house nicely framed along with an autograph of your CEO and so on.
I also join you in wishing him all the very best.