How to specify Internal table field length at run-time

I need to create an internal table where the field length is specified at run-time by the user. Syntax checks because q_pcleng is not a constant. Suggestions for work-around?

parameters: q_pcleng type i default 1024.

data: begin of file_buffer occurs 100,

record(q_pcleng),

end of file_buffer.

TIA,

Kirsten