However, even among those who would agree with me that acts of specific worship ought not be other than what God has appointed will disagree as to the propriety of using hymns or other songs with Christian lyrics outside of specific acts of worship. However, I think (?) most would agree that they can be used so long as not used as specific acts of worship (so car rides, background music, etc., would be fine).
A Facebook comment I made a while back where I try to explain my own view concerning how the 2nd Commandment relates to uninspired hymns from an EP perspective (I agree with Chris about hymns like "Here I am to worship.").
"I agree with your position that hymns ought not to be sung as a specific act of worship to God, even in private; and that the rule for worshipping God is the same in public and in private. However, the way I see it, outside of that setting, I would characterize hymn singing as "meditation" or "religious recreation" (John Brown of Haddington's phrase from his preface to the 1650 Psalter).
The way I see it: Leviticus 10 shows us that the worship that is regulated by God's will is an action that involves "drawing nigh unto God" for the purposes of "worshipping" him (meaning, a "bowing down;" hence, involving a full and complete attention and submission to God's will). An action joined with this movement and with this intent is an attempt to worship by a specific act and must strictly be regulated by God's will. One could make a painting. If however one attempts to draw near to God to worship God either by making the painting or with the painting itself, they are acting against God's law.
As for meditation, it is more inward focused, contemplative; a communing with one's heart; a turning over of one's thoughts; done especially with the intent of stirring one's heart up to worship God (perhaps by prayer or by singing a psalm or portion of a psalm). Meditation is to be performed on all sorts of subjects: God's nature, will, works of providence and works of creation, God's word. Meditation can take the form of a song, as seen, e.g., by Psalm 119. We can thereby also see that although meditation can be found (and ought to be found) in a specific act of worship of God (namely, singing the psalms), a meditation itself is not necessarily a specific act of worship, as it is not necessarily a drawing near to God to worship him.
Some hymns are more meditative in nature rather than an inherent attempt to draw near to God to worship him. Indeed, if one is singing such a hymn while busy with something else, it cannot be viewed as worship: one is distracted by other things and cannot draw near to God with the purposes of worshipping him. Whatever else one might say, if one can find a hymn that is a mere meditation instead of an inherent attempt to worship God in a specific manner, singing or composing that hymn is lawful in that respect. (There may be other reasons to avoid singing hymns though or that might make singing them unlawful; I personally do not sing them.) Intent is also key here as to whether the hymn is being used meditatively or being used as an attempt to worship God by a specific action."