I guess it'd be doable. I've done 1/2 & 3/4 latin through distance, as have some others on the forum.
If you have a good knowledge of ancient greek grammar and accidence, then with some study,
you probably won't have to struggle too hard to learn the latin word forms. Some grammar and syntax
will even carry over, such as accusative +infinitive constructions, passives, middle (deponent in latin),
there's even some similarities in the declensions.
don't get me wrong, it will still take a fair bit of study, but if you've had years and years of classical greek,
then yeah, you could realistically get a 30+ study score in latin if you started 1/2 in 2013 and used your
hols wisely.
or yeah, you could do it at uni. summer latin - 1 year of latin in 6 weeks, takes you to the end of the vce course.