left join with OR optimization

I've seen written that a b-tree index can't be used on a join with an
OR. Is there a way to optimize a join so that it can use an index for a
query such as:

select
a.partid,a.duedate,coalesce(a.quantity,0)+sum(coalesce(b.quantity,0))
from stat_allocated_components a
left join stat_allocated_components b on a.partid=b.partid and
b.quantity>0 and
(a.duedate>b.duedate or (a.duedate=b.duedate and a.popartid>b.popartid))
where a.quantity>0
group by a.partid,a.duedate,a.quantity

Where I am doing a self join to get a running sum, but some rows have
the same due date so I am saying if the due date is the same then the
first one entered should be considered earlier.