As mark mentioned, DH does not offer trac for now.
If you are confident to install it manually, you can follow mark's suggestion to manually install in DH. If you feel that trac does not run very well in DH, you can ask for a refund. (DH guarantees 97 days money back which is true :P)
Be noted that free domain (9.95) is not refundable. You may consider to sign up with a free DH subdomain so that you can get full refund.
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