Change temporary directory without opening R

Question

Today morning when I tried to start R in my Ubuntu machine, I got a new error saying :

Fatal error: cannot create 'R_TempDir'

However when I search over Internet, I realized that my TMP directory is full as below :

df /tmp
Filesystem     1K-blocks     Used Available Use% Mounted on
/dev/vda1       81120924 81104540         0 100% /

There is good discussion available how to change that TMP directory here

Change temporary directory

However, this requires opening R and then change modify the .Renviron file. However since I cant open R now, I cant use above solution to my problem.

So, I am looking for some way to modify the TMP directory to some other custom folder e.g. '/opt/R' without opening R

Any suggestion will be highly appreciated.

Thanks,