I just stumbled on this project ERESI. The project itself looks quite ambitious and supports mainly Intel and Sparc processors with some support for others. There are lots of tools as well that might come in handy. It does have one specific tool that sounds like if fits the bill exactly and quite a few others that are related:
Evarista: A work-in-progress static binary program transformer
entirely implemented in the ERESI language.
Patchelf might come in handy for modifying the linker or rpaths specified in an elf:
PatchELF is a small utility to modify the dynamic linker and RPATH of
Also there is this presentation about injectso which seems relevate to the topic static and dynamic patching of elf binaries. Admittedly the coverage on static binaries is limited but that is to be expected as it is more complex that just being a library interposer.
If you are looking for libraries specifically then the ERESI project does use alot of libraries so you could probably take Evarista as a guide and write something more in line with your goals with thier libraries.
libelfsh : the binary manipulation library used by ELFsh, Kernsh,
E2dbg, and Etrace.
libe2dbg : the embedded debugger library operating within the
libasm : the smart disassembling engine (x86, sparc, mips, arm)
that gives both syntactic and semantic attributes to instructions and
libmjollnir : the control flow analysis and fingerprinting
librevm : the Runtime ERESI virtual machine, that contains the
central runtime environment implementation of the framework.
libstderesi : the standard ERESI library containing more than
100 built-in analysis commands.
libaspect : the aspect library brings its API to reflect code
and data structures in the ERESI language.
libedfmt : the ERESI debug format library which can convert
dwarf and stabs debug formats to the ERESI debug format.
libetrace : the ERESI tracer library, on which Etrace is based.
libkernsh : the Kernel shell library is the kernel accessibility
library on which Kernsh is based.
libgdbwrap : The GDB serial protocol library, for compatibility
between ERESI and GDB/VMware/Bochs/Qemu/OpenOCD.