Coming back to the main idea about Leonard's 70th birthday....
I have an idea..... it is not quite original but with some 'poetic licence' it can be adapted.
The original idea comes from something I saw in a football (soccer) programme which listed the names of ordinary supporters who had 'sponsored' particular items of players' kit in order to raise money for the club.. the club in question being Chesterfield Town.... who definitely need the money. Names of supporters were listed against different players and items of kit e'g shirt. shorts or socks with the shirt commanding the most sponsorship. Any true supporter was proud to be linked to the players in this way.
The modification would be for Cohen fans to 'sponsor' a Cohen song and/or album and some form of 'programme' to list the songs/albums and the respective sponsors.
There would be a minimum sponsorship for each song and album with some albums commanding higher payments and likewise with the songs. In fact it would be fun trying to set a tariff for each. A minimum payment for each would ensure that specific donations are not obvious and that there is something there which everyone can afford, For example Jazz Police...... £1

rising to Suzanne £20 (I'm guessing here, but these would be minimum donations)
There can be more then one sponsor for each song/album. Some songs/ albums might end up with no sponsors

but it doesn't matter
Now here's the good bit.......
Leonard nominates a charity for the money to be paid to.. which I presume we would like to know before the process starts.
Therefore it becomes something which Leonard is involved in to which we respond to. If he was willing he might want to list his songs/ albums in order in readiness for us to set a sliding scale of minimum payments... if not, then I'm sure we could manage to do it ourselves through this forum.
Thinking about it now gives time to do it.
Those who have sponsored will receive some form of publication to commemorate it all and I'm sure that leonard would appreciate the gesture as much as any present... in fact it becomes the present. I'm sure he doesn't want a pair of slippers for his birthday anyway.
This may not be a good idea and I won't be offended if it doesn't grab the attention. If it does take off I will obviously offer to be involved in the practicalities with any willing volunteers.
regards
Pete