[TYPO3-english] Extbase Extension configuration to be written to pageTS for later use in TCA

[Robert Wildling]

Hi,

An extbase-based ext (v6) uses 2 different select fields to grab data 
from two different front-end user groups (fe_groups, fe_users) - at 
least that is the idea.

The problem is: how can I provide a solution for the user to dynamically 
define those user groups, so that the TCA, being responsible for the 
form generation in the backend of TYPO3, has access to that info?

I studied this:
http://typo3.org/documentation/document-library/core-documentation/doc_core_tca/4.6.0/view/1/3/

...and know about markers like ###STORAGE_PID###, ###PAGE_TSCONFIG_ID### 
  etc. They just don't seem to be enough, since I need at least 4 values 
to build the foreign_table_where clause in the TCA:
'foreign_table_where' => " WHERE fe_groups.uid=###FIRST_VALUE### AND 
fe_users.pid=###SECOND_VALUE",

This would be the intended way to go for one field - but, as mentioned 
before) the extension uses 2 fields grabbing info from fe_groups, so 
eventually there will be a ###THIRD_VALUE### and a ##FOURTH_VALUE###, too.

Here...
http://wiki.typo3.org/Extension_Development,_add_Page_TSconfig,_User_TSconfig_and_TS

...I read in the "alert"-section about the new was of imcuding pageTS in 
extbase:
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPageTSConfig($content) 


...but i couldn't find any further, more detailed explanations with 
examples and expecially nothing about how to use those values within TCA.

I also already build a solution based on TypoScript constant values and 
"displayCond" in the BE forms, which works, but it would be most 
cumbersome to reload each and every input 4 times.

And of course: i could just create new tables and voila! But then a lot 
of info would be doubled - this is no way to go!

Any ideas? More sources? Other approaches?
Thanks! Robert