I was expecting this brother!
Let me introduce you to the close enoughs of the languages in the dravidan languages!
Let’s take the instance of asking “What is your name” in each of these languages.
Tamil
உங்கள் பெயர் என்ன (Look at the script) - Which basically reads " Uṅkaḷ peyar eṉṉa?"
Malayalam
എന്താണ് നിന്റെ പേര് ( See the change in the script, it is not even similar. A thousand year difference 
) and which basically read as “entāṇ ninṟe pēr”
Kannada
ನಿನ್ನ ಹೆಸರೇನು ( Just ha ha ha! We have got another script here) And which is read as “Ninna hesarēnu”
So, to answer your query, and we cannot use a more “close enough” language under any circumstance. Just because, the script is so different. Only those people whose learned each language can read its scripts.
Kasargod district is one of the rare districts in India which houses as many as 7 different languages (excluding dialects and tribal languages), with each spoken by a substantial number of people.[10]
The Malayalam spoken here has influences from Kannada and Tulu.
You may ask me that how on earth I managed to write and explain all these three languages. It is because I am from a district in Kerala, whose inhabitants can read and speak in 7 languages. 
. I can understand and read Malayalam, Tulu, Beary bashe, Kannada. I could managed to understand a few words from Marathi and Konkani.
Basically I am man who could converse well in English, Malayalam, Kannada, Arabic, Hindi, Urdu, Tulu, Kannada, Beary Bashe and Tamil 
So to conclude, we don’t have an option of close enough language