I use db_with_handle to connect to non-default pool in ACS 3.4* project, it really works for us, but I never try this on OACS!
You can see this function on
http://yourhome/api-doc/db_with_handle
db_with_handle db code_block
Defined in packages/acs-core/10-database-procs.tcl
Places a usable database handle in $db and executes $code_block.
Parameters:
db
code_block