I think the cleanest solution would be to create a custom Loader
class to wrap flash.display.Loader
and then simply change the import statements in the the project files.
You could even use compiler conditionals if you only wanted to use that class in your mobile project. The compiled desktop/browser project would remain unchanged.
if(CONFIG::MOBILE) {
import Loader;
} else {
import flash.display.Loader;
}
Remember you'd have to define the constant CONFIG::MOBILE
for that to work. Depending on how you compile your code (Flash Builder, Flash Pro, FlashDevelop, etc) there different ways of doing that.