Export latest Titanium Mobile sourcecode:
  git clone git://github.com/appcelerator/titanium_mobile.git

Point codebase to correct Android SDK:
  export ANDROID_SDK=/Users/nilicule/Downloads/android/android-sdk-mac_86

Run scons:
  [ZIPPATH]/scons

Move new SDK to application directory:
  cd "/Library/Application Support/Titanium/"
  unzip "[ZIPPATH]"/titanium_mobile/dist/mobilesdk-1.0.0-osx.zip

This will install Titanium Mobile in the proper directory (mobilesdk/osx/). You can manually do this, too. Either way.
Restart Titanium Developer and select the new SDK version for your project (it's in the Edit Project tab).