Quote from FerdinandAlx:
How does a person borrow physical yen through IB?
Make sure you have a margin account - then either buy any Yen asset (what you would do in this case), or short cash Yen against another currency (what you would do for a conventional Yen-funded carry trade). You will automatically be given a Yen loan to the value of your purchase (or Yen sale) by IB, provided you have sufficient margin to meet it.
Regarding the FX risk:
1) You have your USD starting balance.
2) Buy some Yen-denominated J-REITs
3) Your broker gives you a margin loan in Yen to fund the purchase
4) You now own X Yen worth of stock, and owe X Yen cash. X - X = 0. Hence you have no immediate FX exposure to the Yen rate, at the point of purchase. Your only have FX exposure to the future P&L on the position - and you can just hedge it as soon as it gets to any significant level.
Alternatively, just buy Yen, buy the J-REIT shares, then hedge your exposure with Yen futures or forwards.