Hi Ionut,
I had come across such a requirement recently, My requirement was to add a cell coloring field(type internal table) for ALV.
I solved this by the below code..
CLEAR gwa_fldcat_2.
gwa_fldcat_2-fieldname = 'TCOLOR'.
gwa_fldcat_2-tech = abap_true. " Technical Field
gwa_fldcat_2-ref_field = 'SCOL'. " SCOL type LVC_T_SCOL
gwa_fldcat_2-ref_table = '/BEV2/ED_DETAILS_MATBEL_ALV'. " A Structure
APPEND gwa_fldcat_2 TO git_fldcat_2.
Regards
Sreekanth