Perhaps you could work it this way - between 0 and 360 controls pan, and 400-760 controls tilt. If you send the arduino, for example, 300, it will move the pan servo to position 300, and if you send the arduino 696 it would move the tilt servo to position 296.
That shouldn't be too hard to modify on the existing source, although it would be a bit obtuse to someone not aware of what was going on when looking back, if it wasn't documented well.
Alternatively send a character before each integer string and parse that before you decide what you want to do with the number you receive after it. So P132 would move the pan to 132, and T132 would change the tilt the same amount. A bit more complicated to implement in the C# source code, but by no means difficult.