You may find yourself needing to do process injection outside of metasploit/meterpreter. A good examples is when you have a java meterpreter shell or you have access to gui environment (citrix) and/or AV is going all nom nom nom on your metasploit binary.

There are two public options; shellcodeexec and syringe.

Both allow you to generate shellcode using msfpayload (not currently working with msfvenom) and inject that into memory (process for syringe) and get your meterpreter shell.

shellcodeexec

https://github.com/inquisb/shellcodeexec

http://bernardodamele.blogspot.com/2011/04/execute-metasploit-payloads-bypassing.html

= Short description =

shellcodeexec is a small script to execute in memory a sequence of opcodes.