Hi Anthony,
The custom TSV values may be available in a slice table, but i have not tried it on the portfolio investments objects. Use the following query to determine the table name:
SELECT ID, REQUEST_NAME, TABLE_NAME FROM PRJ_BLB_SLICEREQUESTS WHERE REQUEST_NAME LIKE 'child::<custom tsv attribute>%'
The TABLE_NAME should start of ODF_SSL_nnnnnnnnn
You can then try to retrieve the slice data using the following:
SELECT PRJ_OBJECT_ID subobject_pkid,START_DATE,FINISH_DATE,ROUND((TRUNC(FINISH_DATE) - TRUNC(START_DATE)) * SLICE,2) calculated_sliceFROM ODF_SSL_nnnnnn
This method worked when I created a custom TSV on a Cost Plan Detail but I have never tried it in your situation.