Xthreads field in every Post ?

[Jumper]

Hello,

i think it is not possible, but here is the question:

i need a field in every post (not only start-post), so that the users
can selected something and the start-post is automatically updated.

example:

you have a xthread-field with 10 checkboxes
in post#1 a user selected box#1, box#2 and box#3
in post#2 a user selected box#5 and box#6

now in post#1 the xthread-field show #1,#2,#3,#5 and #6

unrealizable or can i have a little bit hope?