class-bpfb-binder is located in wp-content/plugins/buddypress-activity-plus/lib/
for me, brajeshs hack worked fine so far (beside one single issue of doubleposting, which passed after sparing his very first modification line out). i had the entrybox on the single-profile, and it worked just fine for any written comments. but with activity-plus it was the case, that all mediapostings just showed up until the next refresh. anyway it was correctly posted (i.e. with videopreview) on the main-activity-stream.
so get your class-bpfb-binder.php in that location, then go to line 271 forward. in the first example above was added this "$content = "@" . bp_get_displayed_user_username"... forget this line, as seen in example 2, and add instead:
if (!bp_is_home() && bp_is_member())
$content = "@" . bp_get_displayed_user_username() . " " . $_POST['content'] . "\n" . $bpfb_code;
$content = $_POST['content'] . "\n" . $bpfb_code;
works on 3.5.1/1.7.2
hope that helps :)