Blocking Issue

I have an OLE DB Source from sql server, two lookups and one ole db destination to sql server.  The select in the OLE DB source needs to get a row_number value to create an autoincrementing number that starts at the maximum number already in the destination table in the OLE DB destination task.  If I run more than one month's worth of data (about 25,000 rows) I get blocking from the select for the max id from the fact_destination for the bulk insert.  I have the default read committed isolation on.  In the past I have had the same or similar situation and have resolved it by either just selecting one month at a time or by turning on snapshot isolation but I'm wondering if there is something better I could be doing.  I have tried to look into setting the maximum insert commit size but I think that only affects the batch size so that the trans log doesn't fill up.  I do have the table lock and check constraints selected for the ole db destination task.  Each task has its own connection to the database.  Is there anything else that I can do to be able to select more data without blocking?

Psudocode in ole db source:

set nocount on

declare @main table(column1 nvarchar(50),column2 nvarchar(50),column3 nvarchar(50))

insert into @main

exec storedproc ('1/1/2012','1/31/2012') --takes about 10 min to select data from another db and table

select row_number() over(order by column1,column2,column3)+(select coalsce(max(id),0) from fact_destination) as id

,column1

,column2

,column3

,getdate() as createdatetime

from @main

I would get your max number with an execute sql tak in the control flow before the data flow. Save the max number in a variable and use it in the source query.