So you want to read Solman data from your ECC system, right?
As genric FM like RFC_READ_TABLE don't use the actual structure but map to CHAR 512, you don't need any customer FM. the problem shoulds not be related to RFC, but to creation of an internal table in a system (ECC) using a structure defined in another system (Solman), so not usable in DATA statement of ECC.
So if you don't want to create a similar table/structure in ECC (and maintain it later) you could create a dynamic table, getting information on remote (Solman) structure with a RFC enabled FM like DDIF_FIELDINFO_GET, and creating the local data with cl_abap_structdescr and other RTTS tools as described in many threads.
Regards,
Raymond