How much grain can you mash in your partial?
Option 1:
Find a highly rated AG recipe and replace whatever portion you need to of grain with extract. Full volume boil best, calculate changes if you can't.
Option 2:
A bit more theoretical than I would like to be - If you use a good quality pale malt (grain) and a good quality pale malt (extract - something like weyerman pilsner for both - CB stock weyermann extract), maybe a dose of sugar, a quality fresh lager yeast (people speak highly of the wyeast danish - not used it myself), some hallertauh and/or saaz in 2 or 3 simple additions to around 30 IBU and ferment cool and long then lager for 2+ weeks, , I reckon you'll get as close as you are aiming for.
Mash the grain very low - say 62 degrees.
Even if you go option 1, I would still aim for quality pale extract and mash your grain low
Won't be perfect but it will be a thirst quencher.
To be honest, I reckon my lagers from all grain are my weakest beers - it's a pretty blank canvas but I can happily slam them down on a hot day and happily offer them to friends for the same purpose. Been a while since I made an extract anything but if I were in your shoes, that is what I would try.