One of the possible ways I came up with was:
One of the large web portals like XstreetSL or OnRez should issue giftcards that can be used on their web backends or - in case of OnRez - their in-world vendors. Once purchased, the card could be used for any purchase with any of the listed items - the merchants would get L$ put into their accounts after the purchase.And guess what - exactly this did finally happen!
Since August already you can buy gift certificates on the new marketplace slapt.me, going from 500 L$ up to 10.000 L$. You can give the card to any person, and the recipient can redeem it on slapt.me where their account get credited with the amount. The caveat is - of course - that not only the recipient of the card needs to have a slapt.me account, but that also the range of products available on the marketplace is still far smaller than XStreet SL. However I am convinced that slapt.me becomes one of the leading alternatives to XStreet SL in due course, so that the range of available products will grow over time.