Can i able to share the content posted in subsites to mainsites if database tables are different?

I have a requirement which i have found domain access serving the purpose almost 80%.

My setup is like below.
I have example.com as main site. Database tables are not having any prefixes.
I have one.example.com, two.example.com as subsites. Both subsites database prefixes are
example_1_, example_2_ respectively.
My main site would work as a aggregator and would post the teasers(teasers along with some
two lines write-up) for the node which came from one.example.com, two.example.com.
I have some blocks in main site which do the teasers block job. But it is taking only from main
site database. Not from other subsites.
I thought of following work-arounds,
if you post your content apart from mainsite, it would insert the node in that subsite as
well as mainsite. so the content would be visible/accesible from main site / respective
subsites. That time the blocks what i have would work as per my expectations.
so the need at this moment is , how to designate one particular site as a default site
where the content will be posted in addition to the current active sub domain.

would really appreciate if there are any other workaround.