Use your backup computer. I assume you have a backup computer since your computer is so critical to your jpb. If you don't, get one before sending yours in for repair. Clone the hard drive to your backup computer or at least copy over your data files.
Do not turn over your computer if the only copy of your data is on the computer's drive. Make sure you keep a copy of your data. Not that the repair shop will, but you run the risk of the shop deleting or corrupting your data.
Please be advised that we are individual users just like you. I understand and appreciate that you use your MBP in a vocational environment and evidently it is critical for you to have a functioning MBP at all times. Unlike some car dealers, Apple does not have a 'loaner' program.
You may be able to talk the local Apple store to lend you one, but they are under no obligation to do so. As BobTHeFisherman suggests, the only reasonable solution for the current situation and possible future ones, is to have a backup MBP, ready to be used if the primary one fails.
Even if you got a 'loaner', I question the practicality of setting it up and transferring data in a timely manner that would enable it to be used for your job. The quick and temporary solution to you situation is to purchase an external DVD drive that can substitute for the internal one with the entrenched CD. This should permit you to continue your work uninterrupted with all functions of your MBP still at your disposal.