I've done this for years but I was surprised to find not many people do this. I have two options for this, 1) Straight forward- enter a $5 SNG to use as a tourney cost buffer. If I want to enter a MTT between $11-$22 I often sit in a $5 SNG and try to win my entry fee. Option 2) I start on a Friday with either a $1-$3 (depending on site) and grind up as much as I can either off/on when I want to play or straight hammer till I fall on Saturday. In any case I do this to create funds for Sunday tourneys.
I'm not suggesting that this is always profitable but it does give you some chances to both speed up and slow down. Tourney exercising! While sitting in a top 3 dynamic. As with anything else be honest to your BR and set some limits. Hope this gets you into that MTT you've been eyeing.