The Chaye Adam ([26:4][1]) brings 2 separate answers:

 1. Whereas one may sit not involved in prayer in front of one who is mid-tefila if there is a 4x10 tefach partition, this possibly won't work for a passer unless the partition totally blocks the view of the davener to the passer.
 2. A 4x10 partition will work since we see that one may pass by the view of a davener if he is beyond 4 amos.

The CA gives stronger support to the 2nd answer, though I have seen others pasken like the 1st.

The 2nd answer does not seem to be limited to the CA's alternate reason for the restriction- that the passer-by separates the davener from the shechina (26:3).  Rather, even according to the generally known reason- that passing by distracts the daveners attention, the CA holds that the rabbinic restriction is limited to the domain of the davener.  If his attention will be distracted from beyond the domain, too bad.  Therefore a 4x10 partition in front of the davener would work as well.


  [1]: http://hebrewbooks.org/pdfpager.aspx?req=49397&st=&pgnum=97