BorrowLenses now offers insurance for cameras priced below $4000. Given that you are renting lenses for $900, you should be fine renting lenses now using the insurance BorrowLenses provides for a fee and without obtaining 3rd party insurance.
The challenge becomes if you want to rent lenses priced more than $4000. BorrowLenses (or any other camera rental) will require a deposit for the price of the camera or proof of third party insurance. I spent some time searching and most insurance for rented cameras only provides coverage while on paid gigs. This is unfortunate for those of us that are renting a camera for vacation. Unfortunately, homeowners coverage typically doesn't cover rented property and doesn't provide "inland marine coverage" or valuable cargo that you transport such as an expensive camera lens. Your mileage may vary with homeowners insurance but I would confirm with your agent as it is rarely the case that it will cover expensive camera rentals.
Here is a list of companies that will insure camera rentals. Almost all are restricted to professional photographers or are at a price range (premiums starting at $500/year, $500 deductible or $250 for short-term insurance) that is impractical for most hobbyists:
Arts & Entertainment Insurance
Pro Photographer's Insurance
Tom Pickard Insurance Brokers
Here is a good discussion of insurance solutions from digital photography review