How to make the haeder as bold whiel sending email attachment via cl_bcs class

Hi  Experts,

Need your valuable advice regarding the following..

We are sending a mail with CSV attachm,ent via cl_bcs which will also break the attachment intos eparate csv when the count is 30,

Now They want the header / part of the header of CSV as bold ..

can you please help us regarding the same, currently we are using the following code piece to convert the whole lot to binary content

cl_bcs_convert

=>string_to_solix(
EXPORTING
iv_string = lv_string
iv_codepage = '4103'
iv_add_bom = 'X'
IMPORTING

et_solix = lv_binary_content
ev_size = lv_size ).

lv_string content the header along with all  30 records  of CSV file, intial line will contain the header basically,

Thanks in advance for your valuaable advice..