The Dink Network

Or to make it a bit smoother, use a loop like so:
int &felmx = sp_x(&current_sprite,-1);
int &felmy = sp_y(&current_sprite,-1);
int &fsize = 5;
int &felm = create_sprite(&felmx,&felmy,6,971,1);
sp_size(&felm,5);
sp_brain_parm(&felm, 400);
sp_brain(&felm, 12);
wait(3000);
sp_speed(&felm,1);
sp_target(&felm,1);
sp_base_walk(&felm,970);
loop:
&fsize += 1;
sp_size(&felm, &fsize);
wait(50); //adjest as needed
if (&fsize < 100)
goto loop;

Another posibiliy would be to use the shrink/grow brain but set it larger than you really want and stop it at 100, but that strikes me as likely to mess up unexpectedly.