In IFAF we teach Goal Line first and work back to the Line to Gain if there is one and it's necessary to do so. A lot of our mechanics are influenced by the CFO, so it may be that CFO is similar but I can't find anything definitive in the current manual.
Peter,
This specific issue isn't addressed in the CCA manuals. However, current practice my most, if not all, NCAA officiating groups is to work LTG, if you have one between the B-7 and the GL. However, since the GL is more important than the LTG, many wings I know will work the GL first, if the LTG is between the B-2 and GL. We get spots all the time from beyond/behind BCs, so this is no different. Mark the best spot you can. That's all anyone can ask. But, be in the best spot you can be for plays at the GL.
Easy enough for FBS, either way, knowing that the "eye in the sky" will get involved and fix a bad spot. But, for those in lower level NCAA and other organizations that don't have that luxury, you gotta be in position to rule on the most important line, by whatever means necessary. If you are good enough to work a LTG at the B-1 1/2, then hop to the GL and be set before the ball gets there, by all means, get 'er done. And I have known some that were, in fact, good enough. And others that weren't. Know yourself, and do whatever you need to do to get the job done.