I couldn't find an equivalent for euros, but for US markets the treasury direct alternative is what I prefer. 

Pay minimal rent, perhaps something equivalent to the mortgage payment, so there is no cashflow. 

Trying to find best equivalent to: https://www.menards.com/main/flooring-rugs/vinyl-flooring/vinyl-planks/shaw-reg-citadel-floating-vinyl-plank-5-91-x-36-84-18-14-sq-ft-pkg/mr30000755/p-1444453422201-c-6617.htmLeaning toward: https://www.homedepot.com/p/Shaw-Hamilton-Boulder-7-in-x-48-in-Resilient-Vinyl-Plank-Flooring-34-98-sq-ft-case-HD80300520/304626885

The choices are basically equivalent, so it doesn't really matter which you choose.   

Actually our worst investment is our cash equivalents, but we sleep well at night.   

Your "books" are equivalent to the image below. 

Suppose rents increase at 2%/Yr over the next 30 years, inflation averages 4%/Yr, and your current total rental income is $10,000/Mo, here’s what happens to that income in today’s dollars:In 10: years $8,235 (a 17.65% decrease in buying power)In 20. years: $6,782 (a 32.18% decrease)In 30 years: $5,585 (a 44.15% decrease)So even though your rent increases to $12,190 ($10,000 x (1 + 2%)^10) after 10 years, inflation erodes its value to the equivalent of $8,235 today.

My question is, how do I and my agent to write a purchase contract and absolutely transform a hard money loan into a cash-equivalent offer in the seller's eyes? 

In this scenario, the losers are people holding cash or cash equivalents, saving accounts money market, bond funds and highly leverage banks.  

For example an oceanfront property with a transferrable STR permit went pending in one week..and at least 5/10 of our top luxury STR prospects are off the board..Advice to anyone, anywhere on how to close a (healthy) STR on a tight timeline:- First and foremost - perspective: Acquiring a turn-key (particularly luxury) STR in real estate terms is the equivalent of purchasing a Ferrari.