Starts with a larger ubercart order number
Run this query against your database:

ALTER TABLE uc_orders AUTO_INCREMENT = 100001;


The next record added will use 100001 as the ID.

Or for Postgres (Thanks @Mołot for the heads up):

SELECT setval('SEQUENCE_ID', 100001, FALSE);


You'll need to replace SEQUENCE_ID with the appropriate sequence id for the uc_orders table.

For sequence-enabled databases that lack setval (like Oracle, at least in some versions), you can:

ALTER SEQUENCE schema.sequence_id INCREMENT BY 1000;
SELECT schema.sequence_id.NEXTVAL FROM dual;
ALTER SEQUENCE schema.sequence_id INCREMENT BY 1;