Is it possible to call make install from debian/rules in a launchpad recipe?

The repository is a static library that is a dependency that is not on the ubuntu repositories (and which i would like to get the latest revision anyway).

I'm doing (on debian/rules) this:
#!/usr/bin/make -f
export CFLAGS=" -O3 -fomit-frame-pointer -flto -fwhole-program"
export CXXFLAGS=" -O3 -fomit-frame-pointer -flto -fwhole-program"

%:
 dh $@
override_dh_auto_configure:
#build & 'install' static mt32emu from the nested launchpad repository prior to building dosbox
#remember, each indented line in a rules file is run on a shell (this first line can't be separated)
 cd src/munt;cmake -DCMAKE_CXX_FLAGS=${CXXFLAGS} mt32emu;make;make install
 ./autogen.sh
 dh_auto_configure -- --prefix=/usr --enable-core-inline

It fails with this:
[100%] Built target mt32emu
make[3]: Leaving directory `/tmp/buildd/dosbox-0.74+20121225/src/munt'
Install the project...
-- Install configuration: ""
-- Installing: /usr/local/lib/libmt32emu.a
CMake Error at cmake_install.cmake:36 (FILE):
  file INSTALL cannot copy file
  "/tmp/buildd/dosbox-0.74+20121225/src/munt/libmt32emu.a" to
  "/usr/local/lib/libmt32emu.a".

make[2]: *** [install] Error 1
make[2]: Leaving directory `/tmp/buildd/dosbox-0.74+20121225/src/munt'
make[1]: *** [override_dh_auto_configure] Error 2
make[1]: Leaving directory `/tmp/buildd/dosbox-0.74+20121225'
make: *** [build] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
E: Failed autobuilding of package
I: unmounting /var/cache/pbuilder/ccache filesystem
I: unmounting dev/pts filesystem
I: unmounting proc filesystem
I: cleaning the build env
I: removing directory /var/cache/pbuilder/build//11442 and its subdirectories

if i try to add a sudo build-dep and use 'sudo make install' instead it fails with this:
no tty present and no askpass program specified

Is this possible? I'm aware that i could build it by changing the location of the dependency to not be a 'system' one in the project that requires it; but it would like to keep the changes to the project to the minimum, since the patch i'm using is not mine, and is also from the library repository and is likely to update

(thou i probably can do a 'patch to the patch') edit: this doesn't work, because quilt doesn't allow it.