You can do two one-way tickets. Buy one way into the DR, cheap, on the airline of your choice.
Then buy another one-way, out of the DR, on a DIFFERENT airline, make this one fully refundable. The different ticket needs not to be into your original point of departure, just out of the DR. (E.g. you're a Canadian, you book on Air Canada Toronto to Punta Cana, for your return you will book a refundable ticket on JetBlue from Santo Domingo to Buffalo, NY, for example.)
Make sure the two tickets are NOT on one airline, or even another airline within the same airline alliance. (e.g. do not book a ticket-in on Air Canada and ticket-out on Continental/United). If you read carefully, most airlines' refund policy and contract of carriage (but hey, who reads those, right?) stipulate that refunds are not permitted if the ticket you are requesting refund on, is used as a prof of return or onward travel.
So, the way to get safely around this, is to have tickets on two different airlines, preferably two which are not in the same airline alliance, or using a low-cost (e.g. Jetblue). Your return ticket WILL be accepted by the boarding airline as proof of onward or return travel, but they have NO way of notating or flagging that reservation and/or ticket because it's not theirs!!
Once in the DR, CALL the second airline to request a refund. Most of the airlines also allow refund requests through a web form. DO NOT go to the airline's office or the ticket counter to request a rfund, BECAUSE then the second airline will know what you are up to. So do NOT pay cash for the ticket, book it with a credit/debit card through the airline's website (tickets bought on the airline websites are the easiest and quickest to get refund on).
Good luck!