gistfile1.txt

$ pwd
/tmp/module

$ tree
.
├── fluent
│   ├── __init__.py
│   └── sender.py
└── plugin
    ├── __init__.py
    └── fluent.py

$ cat plugin/fluent.py 
import sys

sys.path.append('/tmp/module/fluent')
print sys.path

import fluent.sender

print 'fluent'

$ cat fluent/sender.py 
print 'fluent.sender'

$ python -V
Python 2.7.2

$ python plugin/fluent.py 
['/tmp/module',(中略), '/tmp/module/fluent']
Traceback (most recent call last):
  File "plugin/fluent.py", line 6, in <module>
    import fluent.sender
  File "/tmp/module/plugin/fluent.py", line 6, in <module>
    import fluent.sender
ImportError: No module named sender

無理矢理

$ cat plugin/fluent.py
import sys

# sys.path.insert(0, '/private/tmp/module/fluent')
# print sys.path

import imp
imp.load_module('fluent.sender',
                open('/private/tmp/module/fluent/sender.py'),
                '/private/tmp/module/fluent/sender.py',
                ('', 'r', imp.PY_SOURCE))

# import fluent.sender

print 'fluent'