You can do that by configuring the client to use dial-up detection only -connection setting. (configuration -> buffer -> keyserver/client -> dialup-link)
Even if you use permanent connection, the client will behave just as you'd like: Keep the buffer topped at the max level.
As for multiple machines, setting up personal proxy was (for me personally) just an unnecessary extra work. A huge amount of work, lol.
So I run my 30 or so machines without pproxy.
Would have been nice to have that 1000 buffer right now though... Soooo much wasted time with the keyserver down.
-S