How do I build custom rpm in scl environment?

Issue

• We are building an RPM that uses DevToolSet-3 (DTS3) for the compilation.
• What's the recommended way to write its SPEC, in particular the %build section?
• METHOD A (just the %build section)

%build
cat <<DTS3_EOF_MACRO | scl enable devtoolset-3 --
./configure <...parameters...>
make clean
make
DTS3_EOF_MACRO

• METHOD B (just the %build section)

%build
. /opt/rh/devtoolset-3/enable
./configure <...parameters...>
make clean
make

Method A is the official way of using scl enable, but it has an annoying drawback: it starts a second shell, and hitting Ctrl-C while a build is running sometimes is not effective (it doesn't kill the rpmbuild).

Method B doesn't have the CTRL-C issue, but I haven't found any RH document approving this methodology.