Is there a compiler option in isCOBOL to extend the length of AREA B in a program source code?

Yes, in version 2019R1 we introduced a new compiler option for this purpose: -sl

This option augments isCOBOL compatibility with other dialects.
It allows AREA B to extend to the end of the line, regardless of line length.
As with other regular compiler options, you need to include it in the compilation string at the command line. Attached is a program called sl.cbl that you can compile using this command:

   iscc -sl sl.cbl

You can see that it compiles successfully. Another way of implementing this is with the IMP MARGIN-R IS AFTER END OF RECORD Directive, specifying

   >>IMP MARGIN-R IS AFTER END OF RECORD 

at the top of the source file.
Also attached is a program called imp-margin.cbl containing this directive in the first line of the program.
You can test it by compiling with this command:

   iscc imp-margin.cbl