It would be quite messy. As soon as a GUI, a database, networking or similar is used, you have a completely different framework, which makes it next to impossible.
While it would still be useful to be able to import BAS and CLS files with "pure code", even that is messy. Differences like VB6 Replace(text, old, new) and B4X text.Replace(old, new), or different base for arrays will mess things up (especially when you make calculations on the indexes).
Just sit down and rewrite. You've already solved the problem once, that's the big part. Now, you just need to re-implement it, that's often surprisingly easy.