if you can spare the interior ankle harness that will speed things up. me i like the harness though.
One of the most popular methods i have heard is to make the upper and lower lacing system one continuous lace system. i have seen or heard of this done by:
1. utilizing just a few of the lower lace loops and then all of the upper lace loops with one lace
2. using a longer lace
The laces for these boots are very long and just simply cutting them to a more manageable length can help alone, which is what i did originally (without making them so short that you loose openness of the boots especially for screwing them on and off the board)
I actually made this video that addresses some of these things (using the D2 for example) http://www.youtube.com/watch?v=sEqVdMyf-K8
is my latest more extreme modification, but a temporary one at that, which does NOT alter the boot in any way other than the removal of the laces. it is a ("free-floating") two strap system similar to the LF vantage, but different too. though i used plastic buckles, a Velcro strap version could be easily made. If you do follow this more "extreme" route and like it, taking the extra step to attach the straps more securely will make them more manageable so they are not so floppy like mine.
here is another, more "extreme" method that might fit your likes that uses a snowboard binding idea. http://www.wakeworld.com/MB/Discus/messages/65919/699495.html
you could continue to use the slingshot boot in the snowboard binding instead of using snowboard boots
you could keep the liners on your feet to eliminate the step of lacing up the liner with the harness. and if you are sharing the boots with another you could toss the liners to the next person in the boat to start putting them on?
maybe you'll come up with another creative idea yourself.
the slingshot boots actually allow for lots of customization IMO