Rewriting HQL to convert right join to left join

Question

I have the following object model:

Account

AccountTransaction
  has many-to-one to Account

PaymentSchedulePayment
  has many-to-one to AccountTransaction

PaymentSchedulePeriod
  has many-to-one to Account

And I want some HQL that will find me all PaymentSchedulePeriod active on the given date and for each one find the latest PaymentSchedulePayment linked to the same account. There may be no payments hence the outer join.

I have a query that works fine:

select p.id, a.id, max( pay.accountTransaction.dttm )
from PaymentSchedulePayment pay right join pay.accountTransaction.account a,
PaymentSchedulePeriod p
where p.account = a
and p.fromDttm <= :date and p.toDttm > :date
group by p.id, a.id

However from this question I was previously having trouble because of the ordering precedence of the joins which was explained in the accepted answer. One of the comments was that to avoid issues like this I should use left outer join instead of right but I'm not sure how to rewrite my HQL to be of the form

from Account left join ... PaymentSchedulePayment

My, possibly incomplete, understanding is that in HQL you can only do outer joins via the object model.

Can anyone suggest how I can rewrite the above as suggested using left rather than right joins?