Lagers, like Sam Adams Boston Lager, aren't a good starting point for homebrewing. They take particular care and attention as well as additional equipment in most cases since they require an extended cold storage to turn out very good.
You do have 1 option though, a beer style called a "California Common" or "Steam Beer" which is essentially a lager style who's yeast strain has been adapted to warmer fermentations. I think if you like lagers, and you want to minimize your bitterness, and get a decent caramel malt background then this is the beer for you. Here's a partial mash recipe I just threw together, feel free to adjust it to your tastes (I'm assuming you're familiar with a partial mash and have the equipment to do so)...
1.00 lb Light Dry Extract (8.0 SRM) Dry Extract 8.3 %
7.00 lb Pilsner Liquid Extract (3.5 SRM) Extract 58.3 %
2.00 lb Caramunich I (Weyermann) (51.0 SRM) Grain 16.7 %
2.00 lb Munich II (Weyermann) (8.5 SRM) Grain 16.7 %
1.50 oz Saaz [4.00%] (60 min) Hops 17.1 IBU
1.50 oz Saaz [4.00%] (15 min) Hops 8.5 IBU
1 Pkgs San Francisco Lager (White Labs #WLP810) [Starter 35 ml] Yeast-Lager
Estimated OG: 1.081
Estimated FG: 1.025
If you need a refresher on partial mashing this is a good article I just found pretty quickly... I'd keep your water/grain ratio down since there's a decent amount of grains for the mash here.
http://www.byo.com/feature/986.html
It's pretty important that you use a Steam beer yeast so that you can ferment the beer in the low to mid 60s rather than the low to mid 50s. Wyeast also makes one, it's number is 2112 (California Lager).
This is an untested recipe but I put it together with a focus on malt flavor while scaling back the hops. As it is now should yield about an 8% ABV beer depending on your yield from the partial mash but you can easily scale the extracts up and down for strength. I don't know if it will be everything that you wanted but in theory it should at the very least be a drinkable beer.
Happy brewing.