loadstring() and loadfile() Lua functions allow loading remote libraries and modules at runtime. As shown in this post it is very simple: How Do I Load Lua Module as a String Instead of a File?
Unfortunately Corona SDK has removed both these function. Here's a list of changes they have.
Is it possible to implement loadstring in lua or load it from a separate module? They seem to provide a solution here but I don't really understand it and I don't think it will work in Corona cause it requires dofile which is also disabled in Corona http://lua-users.org/lists/lua-l/2012-04/msg00875.html